The Manchester United captain made the revelation in his forthcoming autobiography, which is being serialised in two British newspapers.

Haaland was left with damaged knee ligaments after being fouled in the Manchester derby of April 2001 and has not started a game since.

A statement on the Manchester City's official website said: "It has been agreed to jointly instruct a leading firm of solicitors regarding the circumstances surrounding Roy Keane's tackle on 21 April 2001.

"This action has been taken with a view to commencing legal proceedings against Roy Keane and his employers Manchester United Football Club."

Manchester United said they were aware of the development but would not be making any comment.

Keane's tackle earned him a red card but in his book, Keane - The Autobiography, he claims it was pre-meditated and provoked by an encounter between the two some years earlier.

"I waited until five minutes before the end, I hit him hard. I think the ball was there," he is quoted as saying.

"I didn't even wait for the referee to show the red card. I turned and walked to the dressing room."

Keane added he went for Haaland because of what the City player had said when Keane suffered his own knee injury in a tackle in 1997.

"[I told him] 'And don't ever stand over me again sneering about fake injuries.'"