Di Matteo led Chelsea to UEFA Champions League glory after taking over from Andre Villas-Boas, but was sacked after a run of two wins in eight games and with the club on the verge of an early exit from Europe.
But former team-mate Petrescu thinks Di Matteo was harshly treated.
He told fourfourtwo.hu: "I think Abramovich made a wrong decision because Roberto is a really good guy who deserved to stay.
"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."
Petrescu now manages Dinamo Moscow and says he is glad he thwarted Liverpool's bid to sign winger Balazs Dzsudzsak during the transfer window.
The Hungary international, who was courted by both the Anfield club and Inter Milan in January, was forced to stay in Russia when Dinamo could not agree a deal.
And Petrescu is pleased to still have the 26-year-old in his squad.
He said: "Balazs is a class player who is very useful for the team and I'm not surprised he is wanted by the top teams, but this is a good place for him to be.
"He's a really outstanding player and many top teams would like him to be in their squad. That's why I wanted him to stay with us."
Dzsudzsak himself has committed to giving his best for Dinamo after the disappointment of missing out on a move to a big club.
He said: "I did have a good offer that I would have accepted but Dinamo wanted me to stay very much.
"Now I want to have the best season that I can."