The Belgium international sustained the injury against Norwich City in September and has struggled to find his form since returning to action, as he missed a penalty against Everton two weeks ago.
"I don't feel as strong as last season, as I had this injury in the hip," he told Het Nieuwsblad.
"Injuries like that always take more time to heal. I try to compensate it by working harder, but I'm not on my level yet. Don't forget I didn't play for one month.
"I missed a penalty against Everton. I don't look for excuses. I chose a corner, the keeper saved it."
Villa are currently 14th in the Premier League table.