The German international scored 15 goals in the Bundesliga last season but has a release clause of just €12million (£10.5million) which has attracted a lot of interest from teams across Europe.
The 29 year old only moved to Bremen last August from Wolfsburg for £6.4m. He left his former side after a controversy related to leaving £60,000 of poker winnings in the back of a taxi. He was fined a further £20,000 by Wolfsburg after the incident.
Playing for Bremen however, he recovered his form, and his low buyout clause will mean quite a few clubs will be keen to take a gamble on the player.