Marcel Sieberg (born 30 April 1982 in Castrop-Rauxel, North Rhine-Westphalia) is a German former road racing cyclist, who last rode for UCI WorldTeam Team Bahrain Victorious. He turned professional in 2005. He competed in the Tour de France a total of nine times. For the majority of his career, he was one of André Greipel's lead-out men, having been teammates at both Team HTC–Columbia (2008–2010) and then later Lotto–Soudal (2011–2018). In that role he assisted Greipel to over 100 race wins. However, in August 2018 it emerged that the pair would go their separate ways for 2019, with Sieberg signing an initial one-year deal with Bahrain–Merida, taking on a role as a lead-out man for another German sprinter, Phil Bauhaus. He played a role in Bauhaus' stage wins at the 2020 Tour of Saudi Arabia and the 2021 Tour de Hongrie. In June 2021, his team announced that he would retire at the end of the season.