Bayern head coach Jupp Heynckes has refused to be drawn on a time or date as to when he will return to action and he has not been seen since the Champions League win over Anderlecht in mid November.
He came off in that clash with what was described as a ‘minor calf strain’ but he has not been seen since.
Heynckes does not expect the 33-year-old to return for Saturday’s trip to Eintracht Frankfurt.
“Arjen has problems with the sciatic nerve which is a bit inflamed,” he said.
“Normally it’s not a severe injury but a thing of one or two weeks, but we are not able to make a forecast.”
Stoke could face a battle to keep Xherdan Shaqiri as reports have claimed Mark Hughes wants him at Southampton next season.
Bayern Munich have entered the race to Emre Can, who continues to talk up a move away from Liverpool this summer.