Mathias Rasmussen (born 25 November 1997) is a Norwegian professional footballer who plays as a midfielder for Royale Union Saint-Gilloise. After previously playing for the club Lyngdal, he came to IK Start in 2014. On 15 July 2016, Rasmussen signed for Danish Superliga side Nordsjælland. On 10 October 2020, Rasmussen signed a three-year contract with Brann. After a rocky start to his Brann career, Rasmussen became one of Branns most important players throughout his time at the club. After scoring 15 goals and making 10 assists in 28 matches in the 2022-season, he was awarded with the Player of the Year Award in the 2022 Norwegian First Division. On 27 June 2023, with six months remaining on his contract with Brann, Rasmussen signed a four-year contract with the Belgian club Royale Union Saint-Gilloise. The sum paid was reported to be around €1,200,000.