Sepp Blatter, the Fifa president, insisted last night that clubs must release their players for next month's Olympic Games football tournament in Beijing after the newly founded European Club Association (ECA) claimed that there is “no legal obligation” on teams such as Liverpool and Manchester United to recognise the competition.

The tournament in China will leave Liverpool without Javier Mascherano, of Argentina, Lucas Leiva, of Brazil, and Ryan Babel, of Holland, at the start of the season and United will be without Anderson, the Brazil midfield player, and Chelsea will lose Salomon Kalou, the Ivory Coast forward. English clubs appear to have accepted the players' departures as inevitable, but a row in Germany, where Schalke 04 and Werder Bremen are determined to stop Rafinha and Diego respectively joining the Brazil squad, has raised doubts about the tournament's status.

Karl-Heinz Rummenigge, the chairman of the ECA, said yesterday: “As the Olympics are not included in the harmonised international match calendar, the obligation to release players for national team matches according to the Fifa regulations does not apply. We, therefore, support all clubs that face losing important players.”

The issue is clouded by the regulations of the competition, which is essentially an under-23 tournament but with provision for three “over-age” players in each squad. Argentina named Mascherano, the midfield player, as one of three over-age players but accepted requests not to select Carlos Tévez and Lionel Messi from United and Barcelona respectively.

Blatter maintained last night that teams did not have the right to withdraw their players, although his statement appeared not to relate to over-age players. “The release of players below the age of 23 has always been mandatory for all clubs,” Blatter said. “The same applies for Beijing 2008.”

The tournament runs until August 23, ruling players out of the first two matches of the Barclays Premier League season. The departure of Lucas and Mascherano has heightened Liverpool's determination to sign Gareth Barry, the Aston Villa midfield player, but a deal for Robbie Keane, the Tottenham Hotspur forward, is closer.