After the game, a 5-0 loss, manager Brandon Hyde said Mullins suffered a right adductor groin strain and was undergoing further testing.
Mullins, 28, hit a ground ball to shortstop and slowed down short of first base while grabbing at his right upper leg. He left the game immediately after a quick visit from a member of the team medical staff.
Mullins was 0-for-2 with two walks in Monday's game and is batting .263 with eight home runs and 39 RBIs in 53 games. He is a career .263 hitter with 61 home runs and 189 RBIs in 483 career games over six seasons for the Orioles.
Information from Reuters was used in this report.