“When I’m fully fit again I’ll be able to produce better performances. I’m really convinced of that," the German midfielder told the official site.
“I had a couple of problems in pre-season after I joined the club. Then I had two good games for Germany and I picked up the injury.
“I’ll get fit again and I’ll be stronger but that’s all part and parcel of football. I will definitely fight for the club and try to make sure we win every game, as will my teammates. I’ll give 100 per cent.
“The games against City and Tottenham were not my best, because I was struggling a bit with a calf problem in both those games and that meant it was difficult to do everything at a high tempo."