Hannover 96 midfielder Leon Andreasen will be out for roughly six months after his encouraging comeback from a long layoff was curtailed by torn cruciate ligaments suffered in the midweek 4-1 win over Nuremberg, the club said.
The Danish international, who had recently returned from a two-year injury absence, had scored two goals in five league games and another three in the Europa League.
"I suspected something was wrong when it happened. It hurt a lot and the diagnosis is no real surprise," Andreasen told the club website of the injury to his right knee.
"This is a bitter blow, but I have to look ahead and I am sure can come back again," the former Fulham player said. Hannover, third in the Bundesliga, travel to Hamburg SV on Saturday.
Borussia Dortmund forward Marco Reus has been passed fit by team doctors to make his first trip to former club Borussia Monchengladbach since joining the Bundesliga champions, but coach Jurgen Klopp will leave it late to decide whether he plays.
Reus, who joined for 17 million euros in the off-season, twisted his ankle during Wednesday's 3-3 draw at Eintracht Frankfurt and looked set to miss Saturday's encounter.
"I will wait and see how his foot holds up in full training on Friday before deciding," Klopp said.
Dortmund are sixth in the standings, seven points behind unbeaten leaders Bayern Munich.
Bayer Leverkusen defensive midfielder Stefan Reinartz could miss their match against promoted Greuther Fuerth due to a minor groin injury.
Leverkusen are eager to improve their position after their 3-1 win at Augsburg on Wednesday gave them a first victory in three games and lifted the side up to eighth.
Reinartz came off injured shortly before half-time.
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