Venus chases Olympic prize after her year of turmoil

Unlike her sister Serena, who is unbeaten on clay this year and looks as formidable as ever, Venus Williams does not expect to win the French Open. Never in her long career, however, has a fortnight at Roland Garros meant more to the 31-year-old American, whose results here could determine whether she reaches what could be the last great goal of her tennis life.

When Williams was diagnosed last year with Sjogren's syndrome, an incurable auto-immune disease that can cause fatigue and joint pain, it seemed we might have seen the last of the five-times Wimbledon champion. But Williams made it her ambition to return and in particular play at the Olympic tournament at the All England Club.

Following last year's US Open, where she revealed her illness, she changed to a vegan diet, adapted her training and sought to find the medication that would bring her some relief. She is still adjusting to her new regime – the medication can take many months to take effect – and admits that, but for the Olympics, she would not have returned so soon.

"I wasn't really ready to come back, but I had to to play the Olympics and I needed the ranking points," she said. "I didn't have a choice. So I'm just fighting."

Singles players must be ranked in the world's top 56 at the end of the French Open to be sure of making the Olympic starting line-up. With a maximum of four singles berths per country, Williams, who has already won three Olympic gold medals, also needs to ensure there are no more than three of her fellow countrywomen ranked above her.

When she played in her first comeback tournament in March, Williams was ranked No 134 in the world, behind nine other Americans. Given her lengthy absence and physical struggles, her results since then have been remarkable: in two months she has reached the quarter-finals in Miami, Charleston and Rome, beaten four top-20 players in Petra Kvitova, Sam Stosur, Ana Ivanovic and Jelena Jankovic, and climbed 82 places to No 52 in the world rankings.

Crucially, Williams is now the third highest-ranked American behind her sister and Christina McHale, though others could yet overtake her if they outperform her here over the next fortnight.

Asked why the Olympics was such a goal, Venus said: "It's just the ultimate level in sports. It's about participating. It's about having that experience. It's about having the honour to be good enough to be there."

When she was told she had reached her rankings goal, she seemed close to tears. "I don't always feel well, so this means a lot to me," she said. "I've had to get used to how I feel. I've had to get used to a lot of stuff. I have a lot to learn, a lot to figure out. I'm just at the beginning here. I have to make adjustments. Every day is different – and this is probably not going away. All I can do is be positive. You'll never see me down.''

Serena, who shares a house with Venus, has modified her own diet out of sympathy with her sister. She has also seen at first hand how her sister has handled her condition. "It's amazing what Venus has done, it's unbelievable," she said here yesterday. "I don't know anyone out there who has gone through everything that she's gone through and has remained completely positive and yet still played so well.

"To do what she's doing and play a professional sport is, I think, a whole new level of mental strength. I can't imagine personally being in that situation. Everything that she's doing is so inspiring for me."

Serena, who said they had still to decide whether to play doubles together here, added: ''We motivate each other. I think what makes us so good is the fact that we have always had one another throughout our career. We always still have each other and we support one another in our careers.''

Having had her own physical issues in the last two years, Serena agreed she now had "much better commitment" – perhaps as a result of the former world No 1's recent pledge, after some disappointments in her relationships with men, to take a 10-year time-out from dating.

Serena has looked fit and strong during a highly successful clay-court season – she feels "a lot better" after a back problem – and will start the tournament as one of the favourites. "I love being on the court now," she said. "I love every moment. This is what I live for. After going through everything that I went through, I really appreciate every moment more, especially being out on the court."