Keane reveals hip fears
The Manchester United midfielder had an operation on the problem last September but says he still struggles with it and is unable to train properly.
Specialist Ricard Villar performed the operation and told the 31-year-old that he feared he may never get back playing again.
"His (Villar's) exact words were, 'I will be glad if you can get back playing, full stop'. Keane told the Sunday Times. "Is it important to you, Roy, to play tennis with your kids? Do you want to be able to go for a run in the park?
"We discussed the possibility of me having to retire.
"He talked about the likelihood of a hip replacement at a very young age and asked me about life after football."
Keane revealed the full extent of his problem that has troubled him since 2001 as he explained that he was unable to train immediately before and after games.
"That's when the hip injury began to bother me," added the Irishman. "To get through games I would get an injection from our team doctor.
"A jab of Voltarol (an anti-inflammatory) to ease the pain. It got to the point where I was getting them at half-time as well.
"The doctor's advice was always, 'It's not good to be doing this every week', but I wanted to play. It was my decision to have the injections.
"Taken as often as I was taking it, Voltarol was damaging my stomach. For the two days after the injection, the pain would be really bad and I wouldn't be able to train.
"If you're not training, your performance is affected. That's the cycle.
"Last Sunday we played Manchester City at Old Trafford and for the following two days there was no way I could do any training.
"Instead there is a lady who comes into the club and does specialist training work with me the day after the game. I can't train for the two days after a game and for two days before a game."
The former Republic of Ireland skipper also explained that he made the decision to quit international football, and felt let down by the angry reaction of Irish fans.
"This wasn't the manager (Alex Ferguson) or the medical people at the club telling me what to do.
"Don't think for a second this wasn't my decision. It WAS my decision - Roy Keane doing what is best for Roy Keane.
"I feel let down by what has happened in Ireland. I was angry for two days.
"I've cooled off a bit but there's a lot of negative things over there. People need to remember the bloody good things when I played for Ireland."