"Martin O'Neill's teams have always been dangerous at set-pieces and I think I'm right in saying they were highest goalscorers from set-pieces last season," Gregory told the Sunday Mercury.
"Without that they could be one-dimensional. Ashley Young can go past people and provide good quality set-pieces but take that away from Villa's play and there has to be something else.
"I'd love to see a playmaker in midfield who can create something from nothing and show that little bit of guile in the last third. They've got plenty of strength and pace but I don't want Villa to be one-dimensional. It needs to change if they're to seriously break into the top four.
"They need someone to do what Cesc Fabregas does for Arsenal. He picks the ball up off the goalkeeper but also ends up in the opposition penalty box. Reo-Coker is not that type of player and I don't honestly believe that Petrov is the answer. He's a squad player for me, but that's just my personal opinion."