Keane has been dogged by a hip injury

The former Manchester United skipper has indicated that he could cut short his Celtic career as he continues to be troubled by hip problems.

But Petrov hopes Keane will stay and said: "He adds something to everybody's game. He gets 10% more from everybody.

"He always wants to do his best. He always pushes you and he gives the team more concentration."

Keane moved to Celtic Park in January and his influence on the pitch has been increasing in recent weeks.

"He doesn't look like he's got a problem at the moment," added Petrov. "He's been having problems and has told us a few times.

"But every game he looks sharper and we know how important he is for our team with his experience and his name.

"Every time he is on the team sheet other teams wince.

"I hope he will find himself again and will continue to play on for a few more years.

"There is still more to come because he didn't play for a long time before he came here.

"He was injured, but you can see how well he is playing and I hope he is here next season.

"You never know what he might do in the future. He is an experienced player and he knows what he wants."