Behrendt started playing football with local clubs Bremervörder SC and TuS Heeslingen. In 2006, he joined the youth squad of Hamburger SV, but transferred to Rapid Wien at the age of 16 when his father moved to Austria for work. He advanced through the club's youth system and made his debut for the second team in a 3–0 win against SV Mattersburg II in Regional League East on 5 March 2010. He joined First League side SV Horn on loan in January 2013 for the rest of the 2012–13 season.