The German international picked up an ankle injury in a Premier League game against Newcastle in April and has not played since.
He was subsequently left out of Chelsea's UEFA Champions League squad for this season after undergoing two operations to try and cure the problem and he has now told how he feared that he may never play again.
"I had thousands of questions, but I was never given any answers," the midfielder told Die Zeit.
"I'm sure I got on everyone's nerves, but my injury was in my thoughts 24 hours a day.
"Sometimes I thought: You are 31 and have had 14 good years as a professional, maybe it's time to call it a day.
"I thought at first that it was a question of three or four weeks, but then everything started to get complicated.
"First one operation, then another and none of the doctors wanted to tell me when I would be able to play again."