Betts has been sidelined since May 27 with an abdominal strain. He missed the Red Sox’ last 14 games, with the club going 8-6 in that time.
Betts, who is batting leadoff, leads the majors in batting average (.359), on-base percentage (.437), slugging percentage (.750), and OPS (1.187).
Betts also has 17 home runs and 37 RBIs in 48 games.
Without Betts in the lineup, the Red Sox have averaged 4.5 runs a game, down almost a run from their average with him in the lineup.
Shortstop Manny Machado is not in the Orioles lineup Monday.