The German says he underwent surgery over the summer which has caused him to wear the mask so far this season.
"I wear it as a protection for my nose," he said. "I think it's obvious that I had a nose surgery straight after the World Cup.
"I had problems breathing over the last year, so my nose was obviously broken before.
"At the beginning I struggled a little bit. I'm getting used to it more and more, and my breathing is much better.
"Maybe I'm going to wear it for a few more days just for protection and then maybe I can leave it and just play like I did before."