Petit has urged Chelsea's fans to remain patient with their misfiring new arrivals but admitted he has concerns over struggling Havertz.
He told Ladbrokes: "I think moving countries and changing cultures is a big ask - you need to adapt yourself and sometimes it takes longer than people may expect.
"Werner has got the personality to get over this season and turn things around.
"You've got to remember at RB Leipzig he was the central figure in a team largely centred around a counter-attacking brand of football, and that's not a style Chelsea operate with.
"So that's something him and his teammates have to get used to, and that kind of thing takes time."
He added: "Chelsea are a very possession-based club, but when they do play on the counter attack all of a sudden you see Werner's qualities. I've seen plenty of good things from him on the pitch and I'm sure he'll bounce back.
"But Havertz gives me more worries, because of his personality. I know he's very young but I think he's very shy. He needs to fight and show his personality on the pitch."
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