"He tweaked it on that next to last swing and had had some discomfort in the dugout," Showalter said. "We just want to check it out."
A team spokesperson said Markakis will be re-evaluated Wednesday.
Markakis has been one of baseball's most durable players, missing a total of 10 games over the past five seasons. He played in 160 games last season.
Markakis is hitting .256/.333/.452 with eight homers and 26 RBI in 50 games and also has two outfield assists.