Hamburg SV will not be able to count on Croatian striker Mladen Petric in their battle to avoid the drop after the Croatian picked up a muscle injury in training on Thursday and was ruled out for three to four weeks, the club said on Friday.
Petric is the club's top scorer this season with four league goals in 10 games. Hamburg host Kaiserslautern on Sunday.
Hamburg, the only team have played in the Bundesliga every season since the top league's 1963 introduction, managed to climb out of bottom spot with a draw against VfL Wolfsburg last week with new coach Thorsten Fink making his league debut.
Cologne captain Pedro Geromel returned to training on Thursday after recovering from a meniscus surgery in September but the Brazilian said it was still unclear when he could return to action.
"It was great feeling to come back," Geromel told reporters. "Now I can start increasing the intensity of training."
"I can't determine the exact date of my comeback. That will probably be clearer after a few training sessions."
Cologne, who were demolished 5-0 by champions Borussia Dortmund last week, are in 12th place on 13 points and host Augsburg on Sunday.
Bayern Munich midfielder Bastian Schweinsteiger, who missed their midweek 6-0 German Cup win over Ingostadt with a flu, also returned to training and should be fit for their Bundesliga match against Nuremberg on Saturday.
Schweinsteiger was one of six starting players, including Daniel van Buyten, Franck Ribery and goalkeeper Manuel Neuer, who did not play in the Cup, as coach Jupp Heynckes rested them ahead of the league leaders' Bavarian derby on Saturday.
