Serena Williams' coach Patrick Mouratoglou believes the only person capable of stopping the world number one from retaining the French Open is herself.

After defeats in the finals of the Australian Open and Indian Wells, as well as a last-16 exit at the hands of Svetlana Kuznetsova in Miami, Williams won her first title of 2016 at the Internazionali d'Italia in May.

Routine victories over Magdalena Rybarikova and Teliana Pereira at Roland Garros were followed by a difficult third-round encounter with Kristina Mladenovic.

Williams ran out a 6-4 7-6 (12-10) winner to set up a fourth-round clash with Elina Svitolina, and Mouratoglou wants to see the world number one raise her aggression levels.

If she does that, the American's coach is convinced no one can stop her claiming a 22nd grand slam.

"I was not happy with Serena's performance [against Mladenovic], not in terms of level, but in terms of intention," Mouratoglou told

"I think she was not aggressive enough compared to what she used to be and because mentally she was not aggressive enough – because what you do is what you think.

"I don't think she needs to play her best level to win. If I refer to last year, she played far from her best level the whole tournament, she was sick, and she won it, so I wouldn't focus so much on whether she's at her best or not.

"The questions is, is her level high enough to win? The answer is yes. Are her intentions of play high enough to win? The answer is no. But this is something we're going to correct in the next matches.

"We have to take them one by one, find solutions against each of the players, keep the pressure at a certain level that we can control, and then everything's going to be alright.

"I think the only threat is Serena. I don't think anyone can beat her, if she's there, if she's on, if she handles what she has to handle and has the intentions, again, that she's supposed to have, I don't think anyone can stop her.

"I'm sure 100 per cent, no one. So that's the thing we're going to focus on, rather than who can possibly beat her."

On Tuesday, rain caused Williams' last-16 match with Svitolina to be suspended until Wednesday, meaning the world number one faces the possibility of four matches in four days unless Saturday's final is rescheduled.