Petrov said: "The virus is okay. It is better. I've been on antibiotics for the last three or four days and we are expecting every day for it to get better and better.
"I've done a bit of training this morning, I am going to train with the team this afternoon as well to try to catch up.
"I think it should be okay for Sunday.
"In my last game against Burnley at the weekend, I played with a little fever and then I felt really bad after the game.
"I had a lot of pain in my body and my chest was really tight and on Monday I was really bad so I started the antibiotics straight away.
"I've had my chest checked today and it was clear so I can go to train.
"But, even if there had been a doubt, I was going to push right to the end because we have worked so hard as a team to get to that final and nobody would want to miss it.
"If I wasn't fit, the manager could have got someone else to play and I would just have accepted it but I am getting better."
Villa boss Martin O'Neill appears to have no major fresh injury worries, and goalkeeper Brad Friedel, central defender James Collins and striker Emile Heskey will come into contention after being rested for the Palace match.
Reserve goalkeeper Brad Guzan has played in all of Villa's previous matches in the competition this season but has looked uncertain in recent games and O'Neill is likely to choose the experienced Friedel ahead of him.
Villa (from): Friedel, Guzan, Cuellar, L Young, Beye, Collins, Dunne, Davies, Warnock, A Young, Milner, Petrov, Sidwell, Delph, Downing, Agbonlahor, Heskey, Carew, Delfouneso.