FIFA clarify rules over releasing players for Beijing
Blatter has sent a letter to all member associations saying the release of players aged 23 or under is mandatory for the Olympics.
His move comes after two German clubs, Werder Bremen and Schalke, both filed complaints after their Brazilians Diego, 23, and Rafinha, 22, chose to join up with their country's Olympic squad in defiance of the clubs' wishes.
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.
"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.