The Czech goalkeeper's departure to the Bundesliga club concludes a five-and-a-half year stay with the Reds, having joined us in January 2018 from FC Slovacko in his homeland.
Kovar became a regular between the posts for our Under-21s, making almost 50 appearances in Premier League 2. He also featured in the UEFA Youth League on six occasions for the Under-19s.
Earlier this year, he collected a league winner's medal in the Czech Republic at the end of a successful season-long loan with Sparta Prague. He previously gained senior experience during a six-month spell with Swindon Town.
Although the 23-year-old did not make a competitive first-team appearance for United, he did feature in two senior friendlies this summer.