The 24-year-old has refused to commit his future to Schalke beyond the end of the season but when he described reports of a deal with Bayern as "humbug".
Manchester United have watched him as a potential replacement for Edwin van der Sar, but he is not the only name on the English side's short list.
"My future is open," he said. "I've always said that in any case I will play at Schalke until the end of the season."
Just as United are looking to replace a veteran keeper, Bayern need a replacement for 36-year-old Hans-Jorg Butt.