Chen underwent an MRI earlier today in Baltimore.
"Chen is a DL candidate," said executive vice president Dan Duquette. "It's a right oblique strain, and these things take a little time to heal. So, it looks that way. We'll decide tomorrow. But he looks like a DL candidate."
Duquette estimated that it would take "more than a couple weeks" for Chen to return.
"We'll see," he said.
Chen didn't return for the sixth inning of yesterday's game in Minnesota after experiencing discomfort in his right side. He shut out the Twins on five hits over five innings, with no walks and three strikeouts, to improve his record to 3-3 with a 3.04 ERA.
Chen relied mostly on his fastball while unable to get a feel for his breaking ball and changeup. He made it through 73 pitches, 50 for strikes, before leaving the game.
Chen told reporters afterward that it might just be cramping in his side, but Duquette wasn't as optimistic.
"I thought it was a strain," he said. "These things usually take a little time to resolve."
Chen led the Orioles with 32 starts last season and was the only member of the rotation to make more than 20.
Steve Johnson is a candidate to be recalled on Tuesday, since he would be replacing an injured player. He could work out of the bullpen and perhaps make Saturday's start against Tampa Bay at Camden Yards. Reliever Alex Burnett could be recalled under the same rule, since he would be replacing an injured player.
Duquette also listed Jair Jurrjens, who pitched today for Triple-A Norfolk, as a candidate on Saturday.
The Orioles are down to three starters with Miguel Gonzalez on the disabled list with a blister on his right thumb. Gonzalez is expected to make an injury-rehab start Thursday or Friday.
The Orioles have used nine starters this season.
Earlier today, the Orioles optioned left-hander Mike Belfiore to Norfolk.
Belfiore, 24, was recalled prior to Sunday's game in Minnesota, but he didn't pitch. The Orioles needed an extra reliever who could give them lenghth. Belfiore gave them four left-handers in the bullpen, so he didn't figure to stick around.
Belfiore was 1-0 with a 5.52 ERA and 17 strikeouts in 10 games and 14 2/3 innings with the Tides.
A corresponding roster move will be announced on Tuesday, and the Orioles could add a position player. They don't need five starters with the two off-days this week.
"An extra bench player is a possibility," Duquette said.
"We're looking to have the strongest bullpen and bench that we can have."
Note: Left-hander Tsuyoshi Wada will make his first injury-rehab start Thursday at Triple-A Norfolk.
The Tides are playing Lehigh Valley, the Philadelphia Phillies' top affiliate, at 12:05 p.m.
Wada has been pitching at extended spring training. He went seven innings in his last start and struck out 10 batters. He didn't allow a hit or a walk.
Wada is eligible to come off the 60-day disabled list at the end of the month. His rehab assignment can last up to 30 days.