The Italian was given the Blues job permanently in the summer having guided the side to FA Cup and Champions League successes as caretaker manager last term.
However, Di Matteo was then replaced by Rafael Benitez after a run of two wins from eight games earlier this campaign, but Petrescu thinks that the dismissal was harsh.
"I think Abramovich made a wrong decision because Roberto is a really good guy who deserved to stay," said Petrescu.
"He was a good player and everyone could see that he did a great job at the club. I'm really sorry for him and I hope he'll find his place in football."
Chelsea travel to Sparta Prague in the Europa League on Thursday.