You will always be struggling first year after a full knee reco. It takes time to build back the muscle mass let alone the confidence in the leg. That he is improving is a good sign. Hopefully he stays on the same path.
He has definitely overtaken Nasberg as the back-up to Koulierakis as the left-sided center back. It seems Lucescu doesn't want to overload Koulierakis and he rotates him quite regularly, so Michalidis will continue to get a good amount of game-time in the 2nd half of the season.