Sepp Blatter last night stood accused of knowing little about the slave trade and not much more about football after his comments about Manchester United's desire to hold onto Cristiano Ronaldo provoked a furious response. His claim that Ronaldo's treatment at Old Trafford was akin to "modern slavery" prompted leading figures in the game to urge the Fifa President to retract his words. Others, including George Eastham, would be entitled to suggest that Blatter brushed up on his history.

While Blatter's choice of words could not have been more inappropriate in relation to Ronaldo – the Portuguese is believed to earn around £120,000 a week at Old Trafford and has four years remaining on his contract – there was a time, around 45 years ago, when players genuinely were at the mercy of their employers. Eastham, a member of England's 1966 World Cup winning squad, was among them until he challenged the "retain-and-transfer" system in the high court and won.

"It was slavery back then," said Joe Royle, recalling the rules governing transfers when he started his career in the early sixties, a period when clubs could retain a player, often at a reduced wage, and prevent him from signing for anyone else. "If your club wanted you, they had an option to sign you, but you didn't have an option to go where you wanted. If they wanted you to stay they could retain your registration and that's what George Eastham went on strike about all those years ago."

Eastham, who quit football in 1960 after Newcastle refused his requests to join another club, returned to the game the following year, when he signed for Arsenal for £47,000. By then, however, he was committed to improving players' rights – "Our contract could bind us to a club for life. Most people called it the 'slavery contract'," he later said – and, supported by the Professional Footballers' Association, he succeeded in bringing an end to the "retention" aspect of the transfer system.

Since then players have continued to gain the upper hand, no more so than when Jean-Marc Bosman won a landmark case in 1996 which allowed footballers to move freely to another club at the end of their contract. More lucrative salaries, longer contracts and huge signing on fees followed, enabling players to become more powerful, something that seemed to be lost on Blatter as he reflected on Ronaldo's desire to join Real Madrid and expressed his "sympathy" for the player.

Not surprisingly, the Fifa president's remarks were widely condemned. "It just confirms he is out of touch with the issues of professional football," said Richard Bevan, the League Managers' Association chief executive. "Ignoring the nonsensical comparison of a player on £120,000 a week to a modern slave, it is a very poor choice of words. Sanctity of contracts is fundamental to all commercial and employment relationships in that a contract freely entered into is honoured."

Chris Powell, the PFA chairman, claimed Blatter should apologise. "I hope for his sake his words have been taken out of context because to use such an emotive word as slavery and to compare the Ronaldo-Real Madrid-Manchester United saga to slavery is quite ludicrous," he said. "The word has nothing to do with football and for a player to be on a five-year contract and to compare that to slavery is beyond comprehension. I truly hope that Sepp retracts those remarks."

Royle agreed. "He must have a look and see if there has been a redefinition of the word slavery," he added. "Why do players sign contracts? They have to be bound to a contract or we would just have a free for all. Why did Ronaldo sign five years with United? That's not slavery and, if it is, it's self-imposed. Mr Blatter does occasionally come up with stuff which is hard to understand to say the least, but I think he has just about topped the lot here."