 Upon his return to the Camp Nou, Mathieu netted an own goal for Sporting in a 2-0 loss in their final game of the 2017–18 UEFA Champions League groupstage.On 24 June 2020, Mathieu suffered an injury to his left knee during training, which would unfortunately put an end to his career.Mathieu has received caps with all of France's youth teams beginning with the U-15s.