Markakis, who played in 161 games last season, admitted that the injury scared him temporarily.
"At first, yeah, I thought it was broken, because it went completely numb," he said, gesturing to where he got hit. "It went numb for like a minute, but after I got the feeling back, it felt fine."
The former first-round pick was hit in the eighth inning of Saturday night's 3-2 win, and was examined by the team's athletic trainers before he was allowed to continue. Baltimore manager Dave Trembley said before the game that he didn't see the need to give his No. 3 hitter a day off, and Markakis proved him right, homering in his third at-bat on Sunday.
"He's going to hit to see how he is," Trembley said. "If he can't go, I'll put [Jay] Payton in there, but I think he'll be OK. I think there is more concern about his thumb than there is about his forearm. He jammed his thumb sliding into second base. I hope he'll be OK. ... I'd rather have him hit, but if he can't go, I'll take him out. But I'd rather have him play, especially in this park."
Markakis led all Baltimore regulars in batting average (.300), home runs (23) and RBIs (112) last season. He has been pitched around a little more this year, though, and has walked 10 times in his first 11 games.
Spencer Fordin is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.