The 24-year-old has been a regular for the club since arriving at the Veltins Arena in 2011 but suffered the injury in October and has not featured since.
However, he took part in first-team training this week and, while he remains unlikely to feature this term, Hoger said it was a positive step on his recovery.
"I am glad that I was able to complete a full training session with the boys. Now we have to see how it goes, how the knee reacts and how it feels in the next few days," he told the club's official website.
"It is too early to set the exact (return) date now though.
"We will see everything in the next few weeks (but) I will emerge stronger from this difficult time."
Coach Jens Keller was dealt a blow, however, with defender Kyriakos Papadopoulos suffering another injury in training.
The Greece international has been dogged by knee problems in recent seasons and was forced to leave training with a dislocated shoulder, which the club say will be investigated shortly.
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