The Czech Republic international has received criticism over the way Chelsea have conceded goals this season.
But his current manager backed the goalkeeper, who is still only 27, to trust his instincts.
Ancelotti said: "Petr is in good condition. I think that Petr has a fantastic approach. He takes a lot of risks because he likes to go up and catch the ball. I like this.
"Sometimes he makes mistakes but I want him to go and catch the ball in the air."