The French Open was just Williams’ fifth tournament of the year and she was knocked out by Sofia Kenin in the third round.
The 37-year-old struggled on clay, pulling out of the Italian Open due to a knee injury.
Her coach Patrick Mouratoglou admitted Serena Williams was playing through the pain barrier at the French Open.
And the American herself has now admitted the issues with her joint leave her sceptical over whether she will be at Wimbledon this year.
Williams said: “I think she played really well. She literally played unbelievable.
“I was pretty far away – I have not been able to be on the court as much as I would have liked to.
“I will be able to put the time in now. I am glad I came.
“I love the city and the tournament and I really wanted to be here.
“It has just been a really gruelling season for me.
“I hope I have time go get fit for Wimbledon. I am still working on it.
“I think it will be enough time. I definitely hope so.
“I definitely am feeling super short of matches. I have some time on my hands and maybe I will take a wildcard at a grass-court event.”
Pundit Sam Smith believes the Williams was unable to play her best against Kenin due to her lack of fitness.
Smith said: “Great respect from Williams, who knows when she is 60 per cent [fit] she can’t beat someone who is putting on this kind of performance.
“She was beaten out there. She was literally beaten by better tennis.
“She didn’t play horribly, she played OK. Flashes of brilliance, but that’s not good enough when Kenin is playing really lights out tennis.
“She barely missed a ball out there.”