ZURICH, Switzerland — FIFA will issue guidelines by Thursday to calm growing tension between clubs and countries over the use of players for the Beijing Olympics.

FIFA president Sepp Blatter, an International Olympic Committee member, is preparing to rule on whether players must report for national duty if selected for next month's Beijing Games, which conflict with the start of the European season.

Brazil star Ronaldinho has been chosen for China but the 28-year-old midfielder's Spanish club FC Barcelona is refusing to let him go. Brazil is to play the host nation on Aug. 13.

FIFA declined to comment Wednesday but said an official statement from the president's office is expected soon.

Blatter has been an IOC member since 1999 and is a strong supporter of the Olympic tournament.

"For any player, the Olympic football tournament represents a highlight of his career and I hope that a solution can be found," Blatter said in February.

Current FIFA rules obliges clubs to release players 23 and under, but allows them to withhold older players. Each of the 16 competing teams can have three overage players on its roster.

The informal rule is being tested by two German clubs after the announcement of the Brazil squad on Tuesday.

Werder Bremen has refused to release Diego, a 23-year-old midfielder, and Schalke wants to keep its 22-year-old defender Rafinha.

Both clubs say the players would miss preseason training and two Bundesliga games, while Schalke has a Champions League qualifying-round match scheduled for Aug. 12 or 13.