Roy Keane has said that he will not be "losing any sleep" over Sir Alex Ferguson's criticism of him in his new autobiography.

The former Manchester United manager is critical of his ex-captain in his book and claims that the retired midfielder has a "savage tongue".

"I'm okay, quite relaxed," the Irishman told ITV Sport. "I remember having conversations about loyalty when I was at the club and I don't think he knows the meaning of the word.

"To constantly criticise other players that brought him success... I won't be losing any sleep over it. I just don't think the manager needs to do it.

"I don't know how many books he's written now. A lot of these players helped win a lot of trophies. It's just part of modern life. People like to do books and criticise ex-players. I'll have to do another book!"

Ferguson has also been critical of David Beckham, Mark Bosnich and Owen Hargreaves in his new book.