FIFA president Sepp Blatter accused clubs Wednesday of going against the Olympic spirit in trying to stop their players going to Beijing.
"It would appear to be against the spirit of the Olympic regulations to hinder players under the age of 23, who are actually the core of the squads participating in the men's Olympic football tournament, to take part in the final phase of the event," Blatter said in a letter to the 205 member associations of football's world governing body.
"The release of players below the age of 23 (for the Olympics) has always been mandatory for all clubs. The same principle shall apply for Beijing 2008," he said, urging national associations to inform their clubs of the rule.
Blatter spoke out as German clubs Schalke and Werder Bremen prepare to step up their fight to prevent their Brazilian players — Rafinha and Diego — from playing in Beijing next month.
The clubs say the players didn't have their permission to join the Brazil squad in Paris earlier this week to prepare for the Aug. 8-24 games.
Both clubs have pledged to go to sport's highest appeal body, the Court of Arbitration for Sport (CAS) in Lausanne, Switzerland.
CAS secretary general Matthieu Reeb said in a statement Wednesday that "no appeal has been filed and no contact has been made with the CAS by Werder or another club so far."
The clubs say the players are needed for preseason practice, the Aug. 15 start of the Bundesliga season and, for Schalke, a Champions League qualifying match on Aug. 12 or 13.
Their complaint was taken to FIFA by the German national association (DFB) and they won further support Wednesday from the European Club Association (ECA), a new body representing Europe's best and wealthiest clubs including Schalke and Werder.
ECA chairman Karl-Heinz Rummenigge said his members have the law on their side against FIFA.
"(We) support all clubs that currently face losing important players," Rummenigge said. "As the Olympics are not included in the harmonized International Match Calendar, the obligation to release players for national team matches according to the FIFA regulations ... does not apply."
He said this legal point was clarified in meetings with FIFA, which officially recognized the Geneva-based ECA when it was created in January to represent 103 of Europe's top clubs.
Blatter wrote in his letter that the Olympic football tournament had always been treated differently because of its special character.
"This does not mean that there is no release obligation for the relevant clubs," Blatter said.
English club Manchester City accepts it will lose record signing Jo before he's played a game for the club.
The 21-year-old Brazilian striker is in Paris instead of training with Man City, which signed him from Russian club CSKA Moscow for a reported transfer fee of 19 million pounds (US$37.9 million; euro23.98 million) earlier this month.
"We're a little bit frustrated by the fact that he's gone to the Olympics," City manager Mark Hughes said on the club's official Web site. "Ideally, we'd have preferred him to stay with us, but we have to respect that.
"He's part of a very select few players who've been given the opportunity to win the Olympics for Brazil, which they have never done, so I think he'll benefit from the experience."