Celtic signed midfielder Petrov for �2.2m in July 1999

The 26-year-old Bulgaria international handed in an official transfer request on 21 April but it was turned down by the club.

But the former CSKA Sofia player told the Sunday Mail: "I want to test myself at a new level. I'm in a comfort zone.

"I want to play in England. This is not about trying to get more money - this is about my career."

But Petrov, who signed a new contract in January, committing himself to the Scottish champions until 2010, is unsure which English top-flight club would want to sign him.

He refused to rule out the possibility of working again with ex-Bhoys boss Martin O'Neill, who has been linked with the managerial position at Newcastle.

Everton and Fulham have both been tracking him but he said: "There has been interest in the past but I don't know if any side will come in for me.

"To ask to leave one of the biggest clubs in the world isn't a decision you make without a lot of soul-searching. Stilian Petrov

"I have no idea where I will end up. I have not been tapped. I keep in touch with Martin O'Neill and I'd like to work under him again."

Petrov insists that he hasn't taken his decision to quit Celtic Park lightly.

"I hope things can be sorted out with Celtic," he added.

"To ask to leave one of the biggest clubs in the world isn't a decision you make without a lot of soul-searching.

"It was also difficult to tell manager Gordon Strachan. He doesn't deserve it because he is a good man and a good coach.

"But I have to look after myself. I wanted to let him know and that gives him time to plan.

"I hope the supporters understand. I need to find out what I'm capable of. I don't want to be sitting 20 years from now full of regrets."

Petrov, capped 50 times for his country, has helped Celtic to win four titles, while they have also triumphed in the Scottish Cup and CIS Insurance Cup three times during his time at the club.