Marcel Sieberg (born 30 April 1982) is a German former road racing cyclist, who rode professionally between 2005 and 2021 for six different teams. Since his retirement, Sieberg has worked as a directeur sportif for the Team DSM squads and its Development Team DSM, and Tudor Pro Cycling Team and its development team, Tudor Pro Cycling Team U23.

Born in Castrop-Rauxel, North Rhine-Westphalia, Sieberg was, for the majority of his career, 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, and then took on a similar role for compatriot Phil Bauhaus over the final three years of his career at Team Bahrain Victorious (2019–2021), assisting stage wins for Bauhaus at the 2020 Tour of Saudi Arabia and the 2021 Tour de Hongrie. Individually, he took two professional victories – the 2005 Ronde van Drenthe and the 2006 Grote Prijs Jef Scherens.