The Fifa president, Sepp Blatter, was wrong to describe modern footballers as ''slaves'', Uefa said today.

The governing body for European football rejected Blatter's comments that there was a trend towards ''modern slavery'' in the game, with players tied to clubs on unreasonably long contracts. Uefa warned that the increasing power of players since the Bosman ruling in 1995 was unbalancing the relationship between clubs and footballers, rather than an iniquitous system of contracts.

Uefa's communications director, William Gaillard, said salaries were "spiralling out of control", contradicting Blatter's portrayal of exploited players. "It would be useful to remind people that slaves in all of the slavery systems never earned a wage," Gaillard said.

''It seems that both clubs and players are trying to negotiate an exit before the player is free [at the end of his contract]. It is a consequence of the Bosman ruling - there is nothing we can do about that. It is obvious that today players have a lot more power than they did 20 years ago, undoubtedly, and agents have a lot more power than they did 20 years ago," Gaillard added.

Blatter made his remarks in response to a question regarding the future of Manchester United winger Cristiano Ronaldo, who appears to be pressing for a transfer to Real Madrid against the wishes of his club. "There's too much modern slavery, in transferring players or buying players. We are trying now to intervene in such cases,'' Blatter said yesterday. ''The reaction to the Bosman law is to make long-lasting contracts to keep the players, and then if he wants to leave there is only one solution, he has to pay his contract."

Manchester United also condemned Blatter today. A club spokesperson said: "All our players - like at other clubs - enter into their contracts after an open and free negotiation; most of whom do so after taking advice from a Fifa-registered agent. Many do so on a number of occasions and enjoy long and successful stays at Old Trafford.''