In August 2015, Wellenreuther was called up by Germany U21 for the first time. He made his Germany U21 debut on 3 September 2015, starting the whole game, in a 2–1 win over Denmark U21. However, the following year, Wellenreuther was expected to be included in the Germany U23 squad to follow Leon Goretzka and Max Meyer but was dropped from the squad after Schalke 04 did not give the DFB the clearance to allow him to join the squad for the Summer Olympics.