The 32-year-old former Barnsley shot-stopper was sent in for a scan and is expected miss at least three weeks, with rest expected to heal the problem.

"This is good news and we hope that the natural healing process will be enough," team manager Christian Heidel said.

"On the basis of this information we will not be entering the transfer market for a new keeper."

Mueller suffered the injury in a pre-season friendly match with Almennia Aachen last Thursday, which his side won 4-0.

Eurosport