Serena Williams says she is "pretty far away" from her optimal level and may seek a wildcard for a grass-court tournament to prepare for Wimbledon after her early French Open exit.

The three-time champion was stunned by fellow American Sofia Kenin in the third round, losing 6-2 7-5.

It was Williams' earliest Grand Slam exit since 2014 and the 37-year-old now has a month to prepare for Wimbledon.

"I'm working on getting there. I think it will be enough time," she said.

"I haven't been able to be on the court as much as I would have. At least I can start trying to put the time in now."

Williams has not played a pre-Wimbledon grass-court event since Eastbourne in 2011.

That tournament is among those she might be considering before the grass-court Grand Slam begins on 1 July, along with Nottingham, Birmingham, s-Hertogenbosch, Mallorca and Eastbourne.

Since losing to Karolina Pliskova in the Australian Open quarter-finals in January, Williams has played in only three tournaments - Indian Wells, Miami and Rome - and has withdrawn from all of them.

She has struggled with a persistent knee injury since reaching the the US Open final last September and she says she needs more game-time to get back to her best.

"I'm definitely feeling short on matches and just getting in the swing of things," she added. "I don't really like playing out points when I practise.

"I have some time on my hands, so maybe I'll jump in and get a wildcard on one of these grass-court events and see what happens."

The last time Williams, who was seeded 10th at this year's French Open, was knocked out this early at a Grand Slam was at Wimbledon in 2014, when she lost in the third round.

This latest defeat means her bid to equal Margaret Court's all-time record of 24 Grand Slam singles titles continues.

And the seven-time Wimbledon champion admitted she is disappointed by her showing at Roland Garros.

"[If someone had told me I'd come this far] I would have thought they were lying, because I wouldn't expect to have gotten only to the third round," she said.

"So I would have been, like, That's not true."