Cahill returns to Villa Park this weekend and Petrov told his club's website: "Gary has been a rock at the heart of their defence since his move to the Reebok Stadium in January and I notice he even captained the team in the UEFA Cup. That was a great honour for him and it shows how much they think of him.
"Gary never let Villa down when he was here and he only moved on because he wanted regular first-team football. It should make for a fascinating battle with him up against John Carew and Gabby Agbonlahor.
"Injury has prevented Jlloyd making the same impact at Bolton, but he's a quality full-back and I know he's one to watch going forwards."