Mayer is out of the lineup for Thursday's Opening Day matchup with the Reds, Tim Healey of The Boston Globe reports.
Manager Alex Cora indicated earlier this week that Mayer would begin the season in a platoon at second base, so it's no surprise he's on the bench in favor of Isiah Kiner-Falefa with lefty Andrew Abbott on the mound for Cincinnati. Mayer had a .674 OPS over 44 regular-season games in his first taste of the majors last year and batted just .154 versus southpaws.