Borussia Monchengladbach's Patrick Herrmann said he was shocked to discover that he could be out until 2016 after being belatedly diagnosed with a cruciate ligament injury.
Gladbach confirmed on Thursday that Herrmann, 24, had torn the posterior cruciate ligament in his left knee.
The Germany international had sat out two games in August as Gladbach opened their Bundesliga campaign with five straight losses -- a sequence of results that led to coach Lucien Favre resigning.
But Herrmann returned to the starting lineup for wins over Augsburg and Stuttgart, as well as the 2-1 loss against Manchester City in the Champions League.
He then came on as a substitute in last weekend's 2-0 victory against Wolfsburg but still felt that his knee was not quite right.
The midfielder sought further tests, which revealed that he had picked up a much more serious injury than previously thought.
"That was obviously a bit of a shock," Herrmann told Bild. "I did have discomfort but I'm not the type of guy who runs to the doctor over every little thing. We used the international break to do a check-up and this came to light."
Gladbach are hoping that Herrmann will be able to recover within three months.
"After speaking to some specialists, we have decided against an operation," club doctor Stefan Hertl said. "Patrick will undergo conservative treatment and try to make steady progress after the coming four weeks. After that the club and player will decide what happens next."
