And Villa boss Martin O'Neill revealed that leading scorer Agbonlahor also sustained a leg injury during the closing stages of the 1-1 draw, even though he was able to complete 90 minutes.
O'Neill said: "We do have a few injury problems. Petrov will be a doubt for Sunday and he would have no chance if the game had been due to be played today.
"Gabby would be in the same boat. He hurt himself towards the end of the United game. He went down injured, stayed on, but is very sore."
On a more positive note, striker Emile Heskey and left-back Stephen Warnock were able to undertake some running at the club's Bodymoor Heath training complex on Thursday.
Heskey has been troubled by a groin problem while Warnock has been sidelined for three weeks with an ankle problem.
O'Neill said: "Emile did a bit of running and didn't feel any ill effects. Stephen was able to do the same for the first time in a fortnight and we will see how he is on Friday.
"He is a bit more upbeat than he has been and that is pleasing to see."
O'Neill is adamant Villa will field a strong side against Palace, even if Agbonlahor and Petrov have not recovered in time.
He said: "We're going to try to win the game. There might be a couple of enforced changes and I might make another couple as well.
"But overall we still want to compete in the competition. We have reached a Wembley final in one competition and we want to try and do what we can to do as well as possible in another."