Hahn, who suffered a tibial plateau fracture and a lateral meniscus tear in his left knee on Matchday 10, returned to light training on Tuesday, the club confirmed on Twitter.
For his part, Herrmann has been undergoing physiotherapy since tearing cruciate ligaments in October and is continuing to train individually on the training pitch with athletics coach Andreas Bluhm.
"I'm doing a lot with the ball to get back into the swing of things again after a long break," Herrmann said to borussia.de. "The rehabilitation is going well and and knee feels good. I'm talking it week by week and when I have no pain at all, I'll join in with the team."
There were, however, two Gladbach players missing from training ahead of Matchday 19's opener at 1. FSV Mainz 05 on Friday. Jonas Hofmann sat out with sickness while Mahmoud Dahoud was struggling with a cut on the hand.
André Hahn trained individually for the first time since his injury today. Keep up the good work! 💪 pic.twitter.com/VdhmFLAbID— Borussia (@borussia_en) January 26, 2016