Mayer was promoted to Double-A Portland on Sunday, Chris Cotillo of The Springfield Republican reports.
Mayer was on a tear at High-A Greenville to begin the 2023 campaign, slashing .291/.365/.532 with seven home runs, 33 RBI, 23 runs and four steals over 34 games. Boston's top prospect will now have a chance to prove himself at the Double-A level.