He tweaked the wrist in his final at-bat of Tuesday's 8-6 loss to the Blue Jays.
"[It happened on a] swing, I don't know anything else," Markakis said. "I just swung, and it didn't feel good. It's not like I took an awkward swing or anything. I just swung and it didn't feel right."
Markakis will travel with the Orioles to St. Petersburg, where they will start a three-game set against the Rays on Friday, and have some tests performed on the wrist. He will undergo an MRI on Thursday morning and see a doctor in the afternoon.
The 28-year-old is among the more durable players in the sport, having played in at least 160 games in each of the past three seasons, but he had no intentions of playing on Wednesday after the pain intensified.
"I woke up this morning and knew I had no chance," Markakis said. "It was just swollen and didn't feel right. I couldn't pick up a bat or anything."
Markakis also hurt the wrist on a slide a little more than a week ago, but the pain went away, and he didn't tell anyone about it.
Markakis, who considers himself day to day, is batting .256 with eight homers, 26 RBIs and a .785 OPS.