The 22-year-old tore cruciate knee ligaments in his side's 2-1 win over Hansa Rostock on Saturday, meaning he will be out of action for up to six months.
The results of a scan on Sunday confirmed the player's worse fears and ended any lingering hopes he had of convincing Germany coach Joachim Low of taking him to Austria and Switzerland for this summer's championships.
Sinkiewicz last represented his country at the end of 2005, but he was slowly returning to form having played the past eight games for Leverkusen to move back into contention for an international recall.
He is now not expected to return until the latter stages of the first half of the 2008/09 season.
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