World number nine Elina Svitolina, who has won 13 singles titles on the WTA Tour, has been writing columns for the BBC Sport website during the French Open.

The 24-year-old Ukrainian lost 6-3 6-3 to 2016 champion Garbine Muguruza in the third round at Roland Garros on Friday.

In her final column, she talks about her concerns a knee injury may disrupt the grass-court season, what went wrong against Spain’s Muguruza, how living in London has led to British habits and paying 12,000 euros (£10,500) for a young Ukrainian player to have surgery on a serious injury.

The hours after being knocked out of a Grand Slam are not the moments to make rash decisions.

But I’ve been managing a knee injury for a while and against Garbine it felt the same.

So maybe I will need an MRI scan on my knee next week and see what is the best option going into the grass-court season.

Of course there is a concern I might not play on the grass at all if a scan shows something really serious.

But, feeling how I feel now, I think I will have enough time to recover for Wimbledon.

Against Garbine it was very tough to keep focus and concentration – maybe it was the lack of matches at the highest level over the past two or three months.

Before Roland Garros I had only played two matches – losing in Madrid and Rome – since the Miami Open in March.

The problem didn’t get any worse in the match against Garbine though, so that is good.

Grass is tricky because you have to be ready for movements which could maybe damage the knee more.

It has not been easy for the past two months. I need to see where I am now and take my time.

I have to speak with my team and speak with doctors about when I should start playing on the grass.

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‘I was lost on court’

It is tough to say if Garbine is now the favourite to win Roland Garros but she definitely can play well here – obviously she won here three years ago.

It wasn’t an amazing match but she took her chances and served well when she had to.

I made too many unforced errors and too many poor decisions.

Normally my game is about getting balls back and not making many unforced errors. Normally I’m dictating the point.

But I was a bit lost on court. I didn’t feel so good with the decisions I made.

I hadn’t played since Sunday – when I beat Venus Williams – because my next opponent Kateryna Kozlova pulled out of our match on Wednesday with illness.

It’s tough to say if losing serve five times in the first set and only landing 37% of first serves was down to not playing for so long.

She returned well and I was not concentrating on what I had to do.

I have to go back and analyse and see what I did wrong and move forward.

There is no time to be sad. You have to be ready for the next tournament.

I have to be mentally strong. This is a big part of tennis, getting through these moments.

‘Now I drink tea like the British’

As a top-10 player, I have the privilege of being allowed to practise at Wimbledon early so – injury permitting – I can start playing on the grass in plenty of time.

At the moment I am scheduled to play Birmingham and Eastbourne before Wimbledon, but it depends on my health.

I used to live in London and still have an apartment there so I enjoy going back.

I love the city and that will be my base for the grass-court season.

I love the parks, the small cafes, the nice people and the atmosphere. I enjoy simply walking around and spending time there.

My favourite place is Chelsea, by the harbour, that’s really nice.

And I’ve actually started drinking English tea – with milk. In Ukraine we don’t put milk in tea, we only have green tea.

So that’s the most British thing I’ve learned!

‘I didn’t hesitate to help’

Two weeks ago I heard a 16-year-old Ukrainian player called Daria Lopatetska got injured at a 25k event in Rome and her parents couldn’t afford to pay 12,000 euros (£10,500) for her knee surgery.

As soon as I saw the news, I didn’t hesitate before calling them and offering to pay.

It was important for me to react straight away.

I was sad when I heard because it is a very young age to go through bad injuries. It can damage your future.

I think it is important to help the young generation of Ukrainian players because we can’t afford to lose any future stars.

She was happy that I could help and her parents were very thankful.

It is important to help people when you can and I hope she recovers soon because she is one of Ukraine’s rising stars.

Elina Svitolina was talking to BBC Sport’s Jonathan Jurejko at Roland Garros.

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• Alerts: Get tennis news sent to your phone

Roger Federer and Rafael Nadal are safely through to the fourth round of the French Open for a record 14th time.

The pair move ahead of American former world number one Budge Patty for most fourth-round appearances in Paris.

Federer, a French Open champion in 2009, also became the oldest person to reach this stage of a Grand Slam since Jimmy Connors at the US Open in 1991.

The 37-year-old beat Norwegian Casper Ruud 6-3 6-1 7-6 (10-8) and is the first to play 400 Grand Slam matches.

The third seed, who is playing in his first French Open since 2015, will face Argentina’s Leonardo Mayer in the fourth round.

Nadal, who recorded a 6-1 6-3 4-6 6-3 victory over Belgian 27th seed David Goffin on Philippe Chatrier, will play Argentina’s Juan Ignacio Londero.

• French Open: Karolina Pliskova loses to Petra Martic in third round
• Elina Svitolina column: It’s impossible to predict a French Open winner

On course to meet in semi-finals

Federer’s victory over Ruud was fairly routine after the Swiss broke twice in the opener and went on to win nine games in a row, taking a 5-0 lead into the second.

But world number 63 Ruud, playing in the French Open for only the second time, bounced back to break in the third and although Federer immediately broke back, the Norwegian took it to a tie-break.

He saved two match points then had set point at 7-6 in the tie-break but Federer’s experience came through in another straight-set victory.

Nadal was also made to work for his win despite easing to a two-set lead in an hour and 15 minutes.

Goffin, a quarter-finalist in 2016, was broken twice in the first two sets but broke late in the third to take Nadal into an unexpected fourth set.

The Belgian ran out of steam though, as Nadal showed composure to regain his dominance and wrap up the win in just under three hours.

It is only the second time in 17 matches in Paris that defending champion Nadal has dropped a set and he remains on course to face Federer in the semi-finals.

The Spaniard, who is bidding to become the first player in history to win 12 singles titles at any Grand Slam event, last dropped a set against Argentinean Diego Schwartzman in last year’s quarter-finals.

• Live scores, schedule and results
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Emotional farewell for Frenchman Mahut

Elsewhere, Japanese seventh seed Kei Nishikori came through a thrilling five-set battle with Serbian world number 32 Laslo Dere on Court One.

The two-time quarter-finalist won 6-4 6-7 (6-8) 6-3 4-6 8-6 in four and a half hours after coming back from two breaks down in the fifth set and will face French world number 38 Benoit Paire in the fourth round.

Earlier, Frenchman Lucas Pouille, seeded 22nd, lost 7-6 (7-4) 2-6 6-3 3-6 9-7 to Slovak world number 55 Martin Klizan after the match was suspended during the fifth set for bad light on Thursday evening.

Pouille later criticised ticket-holders and told a French radio station: “They’d rather have a glass of champagne than watch the tennis, that’s the main reason they come. They should [fill the stands] with people who want to watch the tennis.”

Compatriot Nicolas Mahut, 37, who was described as tennis’ answer to Benjamin Button in a press conference on Thursday, lost 3-6 7-6 (7-3) 6-4 7-6 (7-3) to Argentine world number 68 Mayer, who faces Federer next.

He was in tears after losing the fourth set tie-break and waved goodbye to the Simonne Mathieu court with his son by his side.

Second-seed Karolina Pliskova of the Czech Republic lost in straight sets to world number 31 Petra Martic in the third round of the French Open.

Pliskova, a semi-finalist in 2017, has failed to progress beyond round three in the last two years at Roland Garros.

The 27-year-old had been in good form, beating British number one Johanna Konta to win the Italian Open in Rome earlier this month.

She is the fourth women’s top-10 seed to exit the French Open this year.

• Live scores, schedule and results
• Alerts: Get tennis news sent to your phone

Croatian Martic, who last reached the fourth round in 2012, will face two-time quarter-finalist Kaia Kanepi from Estonia or Russian world number 68 Veronika Kudermetova next.

Australian Open semi-finalist Pliskova was broken twice in the first set and three times in the second after she made 28 unforced errors and won only 33% of points on her second serve.

The world number two has yet to win a Grand Slam title but reached the US Open final in 2016.