The former Manchester City midfielder revealed that it was his "dream" to play for the Red Devils, but he chose their rivals for the chance of first-team football.
"I was a United fan when I was growing up, as it was in my family," The Mirror quotes him as saying. "I had a trial with United and there was a chance I might go there.
"It was always my dream to play for United, but I felt it was the right decision to join City. I felt I had a better chance of getting in the first team there.
"When I was in City's youth teams I got extra nervous playing against them, and even now I still do."
Villa are in Premier League action against United at Old Trafford on Sunday.