Hertha general manager Dieter Hoeness revealed on Wednesday that Serbian star Gojko Kacar, 21, has again asked to be allowed to travel to Beijing.

The matter is in the hands of CAS after Werder Bremen and Schalke both filed official complaints.

The clubs are upset after Werder playmaker Diego, 23, and Schalke defender Rafinha, 22, left without permission to join up with Brazil ahead of the tournament in Beijing next month.

FIFA have repeatedly insisted that all players aged 23 and under must be released for the tournament, but the clubs do not believe that position holds any weight as the games do not appear on FIFA's official calendar.

Hoeness told BZ: "We expect the CAS ruling in five to six days. If the sports court decides that the players off, we need to think again."

Though CAS has not set a date for the hearings after receiving the filings from the clubs on Thursday, they face a race against time in order to resolve the issue before the tournament is due to kick off on August 6.

In the meantime, Rafinha - who failed to report to Schalke's training camp in order to travel to Brazil's meeting point in Paris - is being fined a reported 25,000 euros per day by his employers for unexcused absence.

The clubs have the backing of the German Football League, who claim that FIFA said back in March that clubs were not obliged to release players.

On Wednesday, FIFA president Sepp Blatter sent a letter to all member associations reiterating the world governing body's stance that player release is "mandatory", but Blatter has also accepted a degree of responsibility for the row that is overshadowing the build-up to the games.

"Maybe we bear a share of the responsibility," he said in comments reported by Kicker. "Maybe the communication was not as it should been."

However, he also expressed disappointment that the clubs had seen fit to file complaints with the CAS.

"I am surprised by the response," he said. "If we in football have a problem then we in football should solve it, and not go before the sports court."

Werder Bremen and Schalke are not the only clubs involved, as Barcelona are monitoring events closely, hoping that they will be able to keep Lionel Messi for their Champions League qualifiers.

In the wake of developments in Germany, the club have strengthened their position and sporting director Txiki Begiristain insisted after Thursday night's friendly against Hibernian that they will not release Messi unless faced with sanctions.

"The FIFA letter doesn't oblige us to do anything," Begiristain said.

"There is no mention of sanctions or punishment for the club, only about the Olympic spirit. But there is nothing else new in it, so it is our understanding that everything else remains the same."