"Having received medical advice from my surgeon and the Celtic FC doctor, I feel my only option is to retire," said Keane in a statement posted on the Celtic website.

The 34-year-old Irishman joined Celtic in January after an impressive career at Old Trafford, winning seven league cups and three FA Cups.

"I would like to send the manager, the staff, players and supporters my very best wishes for the future,” he said.

Though his time with Celtic was brief, the Irish midfielder helped the team secure the Scottish League title, a win Celtic coach Gordon Strachan appreciated.

"Even in his short time with the Club, Roy made a great contribution and played an important part in bringing success to the club last season," said Strachan.

"We were delighted to make Roy’s dream come true when we signed him for Celtic and we were happy when he made our dream come true, by helping us to win the title.

"Keane is one of the greatest-ever players to grace the game of football. Roy’s retirement will be a loss to Celtic and, of course, a loss to football in general."

In 1993, Keane made a then British record 3.75 million pounds move to United. Keane's 12-year career with Alex Ferguson’s side ended after a falling-out with the veteran coach.

Last month, Keane returned to Manchester for a testimonial between Celtic and United, watched by almost 70,000 fans.