Mathias Møller Nielsen (born 19 March 1994 in Gentofte) is a Danish amateur road and track cyclist. He helped his Danish squad claim a gold medal in the men's junior team pursuit at the 2012 European Track Cycling Championships in Anadia, Portugal, and later represented his nation Denmark at the Summer Olympics in London. At the peak of his early sporting career, Nielsen currently rides for the Blue Water Cycling Team and Team Trefor-Blue Water.

Nielsen qualified for the Danish squad in the men's team pursuit at the 2012 Summer Olympics in London based on the nation's selection process from the UCI Track World Rankings. He and his teammates Michael Mørkøv, Rasmus Quaade, and Casper von Folsach surpassed the Spaniards by a short distance gap for a fifth-place finish in their final match at 4:02.671.