Tuesday's Carling Cup defeat by Liverpool was new boss Andre Villas-Boas's fifth loss in his last nine matches, and he now faces a make-or-break spell of three games in nine days against Newcastle, Valencia and Manchester City.
But Ancelotti, whose sacking in May opened the door for the 34-year-old Portuguese, said: "Villas-Boas cannot work miracles. This is an old team now.
"The problem is not Villas-Boas, it is with the team that he has.
"Andre is young and inexperienced, but he has done well and he is talented.
"I feel Roman (Abramovich) needs to give him time to sort it out and make his ideas work."