Orioles manager Brandon Hyde, who made the announcement after a game at Tampa Bay on Saturday, said Mancini "is going to miss some time" but didn't say how much.
Mancini took to Twitter on Sunday to show his gratitude for the support he has received.
Once there is more clarity, I will be sure to keep everyone updated over the next few days. I look forward to a healthy recovery and being back on the field soon!— Trey Mancini (@TreyMancini) March 8, 2020
The 27-year-old Mancini, who hit .291 with 35 home runs and 97 RBIs in 2019, has played only five games this spring after earlier dealing with flu-like symptoms.
Mancini last played on March 2, but left the game after two at-bats.
"We love Trey, and we're going to respect his privacy in this thing, and we'll have more information as we know more," Hyde said.
"I think, like anybody else would, that he's going to go have further tests done. All I can say is we're thinking about him. We're just going to respect his privacy in this whole thing. We hate to see Trey miss time, but hopefully it's not too long."
Baltimore opens the season on March 26 against the New York Yankees.