Roy Keane has warned his Barclays Premier League counterparts that loyalty works both ways amid the rumbling row over Real Madrid's pursuit of Cristiano Ronaldo.

The Manchester United midfielder's future has been the subject of fevered speculation all summer, with the Old Trafford club's furious response to Real's interest sparking FIFA president Sepp Blatter's slavery comments last week.

However, while Sunderland boss Keane has some sympathy with clubs whose players are being targeted by predators, he insists they are themselves sometimes guilty of treating players like "pieces of meat".

He said: "I don't really know what is going on at United with Ronaldo and I wouldn't like to comment on it, but there have been other cases and other situations.

"I do believe, generally speaking, it works both ways. Players have been accused of being under contract and asking to leave - there have been cases over the last few years where players have refused to play.

"There was a player who went on strike a few years ago at Forest - did Mr (Pierre) van Hooijdonk go on strike?

"Maybe that's a bit to the extreme, don't get me wrong, but you talk about contracts - what does a contract mean?

"If a player wants to leave, all he has to do is come in every day, not train with the right attitude and I guarantee you that would p*** any manager off, so there are ways of doing it.

"But on the other hand, if the club want to get rid of you and you have got a two-year contract, they will get rid of you.

"I know some top players who have been forced to train with the reserves and do this and do that, so it works both ways.

"Clubs have got to be very careful when they start questioning players' loyalty because when clubs want to get rid of you, they get rid of you.

"I am 50-50. I am the manager of a football club now, but it only seems like yesterday I was playing.

"But loyalty - that word is used in football far too often. Some people talk about it, but they actually don't practice it.

"I don't think there's much loyalty left in football, unfortunately, from my own experiences."

Keane diplomatically declined the opportunity to elaborate, although he has spoken in the past about his disappointment at the way his departure from Old Trafford was handled initially.

But he admitted he would not stand in the way of a player who wanted to leave his club, provided the deal was right for his employers.

He said: "If a player wants to move and go on to better things - I am talking about any player - then I would say, 'Go for it' because when a club are finished with you, they get rid of you.

"Forget about 'this club's being loyal to players' and all this carry on, it works both ways.

"If a player came to see me and said, 'look, I have got a better opportunity' and we got a good deal, I would say 'good luck'.

"Clubs buy and sell players. Clubs sell players sometimes like a piece of meat, so if a player want so to go and better himself, good luck to him.

"When clubs are finished with you, it can happen very, very quickly.

"This word 'loyalty' is thrown about far too easily and some people haven't got a clue what the word means."

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