Gemmer made his official debut for Midtjylland on 29 August 2013, in a Danish Cup match against Vendsyssel when he was just 17 years old.
[9] He was first loaned out to Danish 1st Division club Horsens in January 2016 for the remainder of the season, where he made his debut against Vejle on 20 March 2016.
[13] The week before, Gemmer's teammate from AC Horsens, Nicklas Dannevang, also joined the club.
[15] After a trial with Horsens, the club announced on 27 August 2019, that they had signed a three-year contract with Gemmer.
[16] He was immediately loaned out to newly promoted Danish 1st Division club Kolding IF to regain match fitness after his anterior cruciate ligament injury.