Petrov again started Saturday's home game against West Ham on the bench. He eventually replaced matchwinner Gardner and his arrival was given a mixed response from Villa fans.
Gardner was aware of the reaction and said: "I don't know who or what the fans were booing for. We got the three points, so the substitution was the right decision.
"If I'd have stayed on, we might have lost 2-1. Stiliyan found it hard last year, but he's a great player and I'm sure he'll prove it this year."