Sepp Blatter has reminded clubs that it is 'mandatory' for them to release players aged 23 and under for this summer's Olympic Games.
The Fifa president has written to all 205 member associations in an attempt to quell the growing discontent from a number of sides at the loss of key players for the tournament in China.
Werder Bremen and Schalke have threatened to take the issue to the Court of Arbitration for Sport after seeing Brazilian duo Diego and Rafinha called up by their country.
But Blatter said in his letter: "The release of players below the age of 23 has always been mandatory for all clubs. The same principle shall apply for Beijing 2008."
The fact that this tournament is not included in the co-ordinated international match calendar "does not mean that there is no release obligation for the relevant clubs," he added.
He continued: "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 confirmed that it was not compulsory to release players over the age of 23 - three are allowed per squad - but appealed for goodwill from clubs.
Liverpool are set to lose Javier Mascherano to the Argentina Olympic squad, despite the fact he is 24.
Manchester City's new Brazilian striker Jo, who is 21, has been selected and while manager Mark Hughes would prefer to have his £19million signing available, the club have made no attempt to prevent him going.
Hughes told the club's official website: "We're a little bit frustrated by the fact that he's gone to the Olympics, ideally we'd have preferred him to stay with us, but we have to respect that. It's a high-profile competition and we look on it as something positive.
"The type of players Brazil are taking with them show that it's viewed in a great light in their country.
"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."

Latest Sky Sports News Report
West Ham v Everton - 1st Half
Wigan v Fulham - 2nd Half
Wigan v Fulham - 1st Half
West Ham v Everton - 2nd Half
Chelsea 1-0 Man Utd - Ferguson
Chelsea 1-0 Man Utd - Ancelotti
West Ham 1-2 Everton - Zola
| Time | Fixture |
|---|---|
| Monday 9th November | |
| Barclays Premier League | |
| 20:00 | Liverpool vs Birmingham |
| Saturday 21st November | |
| Barclays Premier League | |
| 12:45 | Liverpool vs Man City |
| 15:00 | Birmingham vs Fulham |
| 15:00 | Burnley vs Aston Villa |
| 15:00 | Chelsea vs Wolverhampton |
| 15:00 | Hull vs West Ham |
| 15:00 | Sunderland vs Arsenal |
| 17:30 | Man Utd vs Everton |
| Sunday 22nd November | |
| Barclays Premier League | |
| 13:30 | Bolton vs Blackburn |
| 15:00 | Tottenham vs Wigan |
| 16:00 | Stoke vs Portsmouth |
| Wednesday 25th November | |
| Barclays Premier League | |
| 19:45 | Hull vs Everton |
| 20:00 | Fulham vs Blackburn |
| Saturday 28th November | |
| Barclays Premier League | |
| 15:00 | Blackburn vs Stoke |
| 15:00 | Fulham vs Bolton |
| 15:00 | Man City vs Hull |
| 15:00 | Portsmouth vs Man Utd |
| 15:00 | West Ham vs Burnley |
| 15:00 | Wigan vs Sunderland |
| 17:30 | Aston Villa vs Tottenham |
| Time | Result |
|---|---|
| Sunday 8th November | |
| Barclays Premier League | |
| Chelsea 1 - 0 Man Utd | |
| West Ham 1 - 2 Everton | |
| Wigan 1 - 1 Fulham | |
| Hull 2 - 1 Stoke | |
| Saturday 7th November | |
| Barclays Premier League | |
| Wolverhampton 1 - 4 Arsenal | |
| Man City 3 - 3 Burnley | |
| Tottenham 2 - 0 Sunderland | |
| Blackburn 3 - 1 Portsmouth | |
| Aston Villa 5 - 1 Bolton | |
| Wednesday 4th November | |
| Barclays Premier League | |
| West Ham 2 - 1 Aston Villa | |
| Sunday 1st November | |
| Barclays Premier League | |
| Birmingham 0 - 0 Man City | |
| Saturday 31st October | |
| Barclays Premier League | |
| Man Utd 2 - 0 Blackburn | |
| Sunderland 2 - 2 West Ham | |
| Portsmouth 4 - 0 Wigan | |
| Bolton 0 - 4 Chelsea | |
| Stoke 2 - 2 Wolverhampton | |
| Fulham 3 - 1 Liverpool | |
| Burnley 2 - 0 Hull | |
| Everton 1 - 1 Aston Villa | |
| Arsenal 3 - 0 Tottenham | |
Skysports.com looks at the best and worst moments from the latest round of top-flight fixtures.
Have a read through the skysports.com debate on Chelsea's 1-0 win over Man Utd at Stamford Bridge.
Pictures from Sunday's Premier League action where Hull snatch victory and Chelsea beat Man United.
Sir Alex Ferguson insisted John Terry's winner should not have been allowed to stand after Man United's defeat at Chelsea.
A John Terry header proved the difference as Chelsea beat Manchester United to move clear at the top of the Premier League.
Carlo Ancelotti admitted his delight in beating Chelsea's "best opponent" at Stamford Bridge.
Wes Brown feels Chelsea's winning goal should not have stood as he insists he was fouled by Didier Drogba.
Darren Bent is in the England squad to face Brazil, while Stephen Warnock and Tom Huddlestone have also been called up.