Sepp Blatter have accused Manchester United of 'modern slavery' and believes Cristiano Ronaldo should be allowed to leave.

The Portugal winger is one of the hottest properties in the sport after a superb season at Old Trafford last term and speculation about a move to Real Madrid has dominated the summer's transfer gossip.

"The important thing is, we should also protect the player," he told Sky News. "If the player wants to play somewhere else, then a solution should be found because if he stays in a club where he does not feel comfortable to play then it's not good for the player and for the club. I'm always in favour of protecting the player and if the player, he wants to leave, let him leave."

Blatter believes the issue raises interesting questions about the way transfers and contracts are dealt with in the game.

"I think in football there's too much modern slavery in transferring players or buying players here and there, and putting them somewhere," he continued.

"We are trying now to intervene in such cases. The reaction to the Bosman law is to make long-lasting contacts in order to keep the players and then if he wants to leave, then there is only one solution, he has to pay his contract."