"It's never happened to me before and I can tell I had a really good first four innings, and I definitely feel good physically," said Chen, who said postgame he wasn't in any pain. "Unfortunately in the fifth inning, I don't know what happened."
Oblique strains typically mean a trip to the disabled list, and losing Chen for any length of time would be a major blow to an already inconsistent Orioles rotation. Chen, who entered the game 2-3 with a 3.40 ERA, was the team's most reliable starter last year. He was the only pitcher to start at least 20 games and had turned in five quality starts in his first seven games in 2013.
"I don't think that happens," Chen said of going on the DL. "It's not that serious to me. I think it's just a cramp and we'll see what's going to happen tomorrow. We will re-evaluate tomorrow, and hopefully it's just a cramp."
"I didn't hear oblique, I'm hearing a cramp maybe," said manager Buck Showalter. "[Head athletic trainer] Richie [Bancells] thinks it's going to be one or the other. We'll take a look at it tomorrow and see where we are, get an evaluation. I'm only thinking good things."
The 27-year-old Chen held Minnesota to five hits and struck out three before he was replaced by right-hander Tommy Hunter. The injury-shortened outing gave the Orioles -- who added reliever Mike Belfiore before the game to help the bullpen -- their third consecutive start of fewer than six innings.
"Regardless of what happens, we feel like we have some people below who are capable of helping us," Showalter said. "I hope we don't have to do that. I'm going to think good things. I was just telling Wei-Yin that. It feels a little better now.
"Hopefully, it was a cramp. You guys know the experience with this, what the percentages probably lay with, but I try not to get into that half-empty thing. I'm expecting something good, and we'll go from there and make the adjustment if we don't."
Brittany Ghiroli is a reporter for MLB.com. Read her blog, Britt's Bird Watch, and follow her on Twitter @britt_ghiroli. This story was not subject to the approval of Major League Baseball or its clubs.