Petrova has lost in the French Open first round for two years running

Petrova, who pulled out of the Italian Open with a back problem, struggled with her movement and had treatment at the start of the second set.

The 24-year-old will have an MRI scan and fears she could miss Wimbledon.

Fourth seed Jelena Jankovic booked her place in the second round with a 6-2 6-2 thrashing of Stephanie Foretz.

The world number five converted four of her five break points in the opening set before breaking her opponent a further three times in the second.

She sealed the 68-minute win with a smash on her first match point.

"I was a little bit nervous today," said Jankovic, who was broken twice in the first set.

I don't want to miss the grasscourt season again Nadia Petrova

"You don't play your best tennis in the first match but I'm getting used to the atmosphere and to the courts.

"I was a little bit slow and the balls were quite heavy but it's good the get past the first round and, hopefully, I'll get better and better."

Jankovic insists she is over the illness which forced her to pull out of the Strasbourg semi-finals last week.

Petrova, who reached the French Open semi-finals in 2003 and 2005, missed Wimbledon last year because of a hip injury.

"I am trying to stay positive in my head, but I really don't know if I will be okay," she said.

"I just really hope that in the end it's not that serious. I don't want to miss the grasscourt season again."

Meanwhile, sixth seed Nicole Vaidisova also won through after beating Emmanuelle Gagliardi 6-4 6-3.

Vaidisova, who reached her first Grand Slam semi-final in getting to the last four at Roland Garros last year, wasted a total of seven break-point chances before claiming the crucial break in the 10th game.

The 18-year-old Czech surged into a 3-0 lead in the second set only to be broken in the fifth. She broke back immediately and although she failed to convert three match points, she sealed victory on her fourth.

Vaidisova has not played since late April because of a wrist injury but said: "I don't have to think anymore about the wrist.

"Of course I'm lacking some matches. But on the other hand, it gives me no pressure here. I can just surprise myself, play better than I expect to and we'll see.

"I haven't played in a while and it's always tough coming back, first tournaments. I just want to be healthy. That's my main concern, being able to play without thinking about anything else."

Elsewhere, 13th seed Elena Dementieva of Russia was too strong for Germany's Angelique Kerber, winning 6-3 6-2.