Hannover 96 striker Mame Biram Diouf has been ruled out for the final four league games of the season with an ankle ligament injury picked up in their 2-0 win over VfL Wolfsburg on Wednesday, the club said.
The Senegal international, who joined in the winter from Manchester United, has established himself as the number one striker after scoring six league goals and four more in the Europa League.
Hannover, in seventh place on 44 points, are battling for a spot in next season's Europa League again.
Hamburg SV, who take on Hannover on Saturday, will be playing with their backs to the wall to avoid relegation, Hamburg coach Thorsten Fink warned.
Hamburg are the only top-flight team to have played in the Bundesliga every season since its creation in 1963.
"On Saturday everyone in the stadium, including Hannover, must see a team that is battling against relegation," Fink told reporters. "We will not stop working."
Hamburg were crushed 4-0 by Hoffenheim on Wednesday to remain on 31 points in 14th place, just two points above the relegation play-off spot.
Cologne defender Andrezinho will be out of action for an estimated six months after undergoing surgery this week for a cruciate ligament tear, the club said.
The 30-year-old Brazilian, who will miss the final four league games as Cologne battle to stave off relegation, was injured during training earlier this month.
Cologne, in the relegation play-off spot in 16th place, travel to fourth-placed Borussia Monchengladbach on Sunday.
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