Roger Federer is no certainty to play the French Open as concerns continue to linger over his fitness.

>Federer loses to Thiem in Rome

The Swiss maestro suffered a 7-6 (7-2) 6-4 loss to Dominic Thiem in the Internazionali d'Italia third round on Thursday.

Federer withdrew from the previous week's Madrid Open due to a back injury and there are fears the 34-year-old could miss Roland Garros.

The 17-time grand-slam champion said he would skip the year's second major, which starts on May 22, unless his health improved.

"Now obviously time starts ticking more towards Paris," Federer said.

"The next 10, 12 days are going to be really important for me to recover. Then, I'll make a plan, I guess today, what the recovery and practice plan is going to be.

"Clearly the way I'm playing right now is never going to be enough for any good run in Paris, and then I also wouldn't play this way.

"I'm still confident I will be fine somehow."

The last time Federer was absent from the main draw of a major was the 1999 US Open – a run of 65 consecutive slams.

However, Federer, who underwent knee surgery earlier this year, took some positives out of his Rome exit.

"I'm happy I'm through the tournament now and can look ahead. I can pace myself," he said. "In a match you can't really pace yourself."