The 23-year-old felt the injury grab in the third inning of his start at Camden Yards and nearly attempted to work through it. Winless this season, Kennedy considered trying to head back out for a fourth inning after the Yankees took an 8-4 lead in their eventual 10-9, 11-inning loss, but said the pain was too much to bear.
"I was just trying to take deep breaths, and after a couple of seconds, it went away," Kennedy said. "It allowed me to throw another pitch and I got two outs, so I just tried to get through that inning. I was trying whether to decide to say anything and it was just too painful to go through."
Yankees manager Joe Girardi said the team will place Kennedy on the 15-day disabled list. He was charged with four runs on four hits against the Orioles in his eighth start and ninth appearance of the season, allowing back-to-back home runs to Kevin Millar and Ramon Hernandez in the second inning. Kennedy also threw a wild pitch, walking none and striking out three.
"It's an injury that we feel he won't be able to make his next start," Girardi said. "He possibly wouldn't be able to make the start after that. We can't go with four starters, so we're going to have to do something."
That "something" may include having Joba Chamberlain take Kennedy's next turn in the rotation on June 2, though that topic will be discussed by Girardi and general manager Brian Cashman following Chamberlain's scheduled relief outing on Wednesday at Baltimore.
"We'll have to have discussions to see," Girardi said.
For Kennedy, the injury represents another abrupt interruption to his rookie season. Kennedy made the Yankees' Opening Day rotation out of Spring Training but was shipped to Triple-A Scranton/Wilkes-Barre for a two-start stint, where he was to tweak his mechanics and regain confidence.
Kennedy said the injury was similar to the strained upper back muscle he suffered while throwing a bullpen session prior to a Sept. 22 scheduled start last season, costing him the remainder of the year and a spot on the American League Division Series roster.
"It was weird, because I didn't get any signs of it," Kennedy said. "It just came up and kind of grabbed in my lat area. It's really similar to last year, but I would say it's a lot better, because last year it was more my back and my lat. This makes me think it's a lot better because it doesn't hurt as much when I breathe."
The Yankees' first-round selection in the 2006 First-Year Player Draft, Kennedy is 0-3 with a 7.41 ERA. In 37 2/3 innings, he has allowed 41 hits and 32 runs (31 earned), walking 25 and striking out 26. The Yankees are also without touted right-hander Phil Hughes, who suffered a cracked rib last month and is not expected to be available until July.
"It's not what you like to see, but you know that injuries are part of the game," Girardi said. "When you look at Phil's, it's a strange injury. He'll be back and Ian will be back. We'll get them going."
Bryan Hoch is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.