Duhnke played youth football for FV Karlstadt and
1. FC Schweinfurt 05 before joining the
Bayern Munich Junior Team in 2008, at the same time that his older brother,
Manuel, was signing for the
reserve team. He scored prolifically for Bayern's youth teams, including six goals in 35 minutes in an under-17 match against
1860 Munich in 2010, which Bayern won 8–0. Marius was promoted to the reserve team two years later, although Manuel had since moved on, and made his debut on the opening day of the 2012–13 season, as a substitute for Fabian Hürzeler in a 1–1 draw with
FC Augsburg II in the
Regionalliga Bayern. He ended the season as Bayern Munich II's top scorer, with fifteen goals, fourteen of which had come in the second half of the season, as the team finished in second place. Despite this, though, Duhnke left Bayern in July 2013, believing he had little chance of breaking into the first team, and signed for
SpVgg Unterhaching of the
3. Liga. He made his debut for the club on the opening day of the 2012–13 season (his 20th birthday) as a substitute for
Janik Haberer in a 0–0 draw with
Jahn Regensburg. ==Career statistics==