"We improved our offer once again, but Ivan unfortunately decided not to accept it," Bremen sporting director Klaus Allofs said.

"We had expected a different outcome, because he is a superb forward who has proved his class at the highest level, despite his kidney transplant."

The 28-year-old missed large parts of the season after having a successful kidney transplant.

He filed lawsuits against two of Bremen doctors for failing to provide him with an adequate medical care.