Holland went on the 15-day disabled list on Saturday with what was termed a left rib stress reaction. Right-hander Jeremy Jeffress was recalled from Triple-A Omaha to replace him.
On Friday night, Holland came in to protect a 2-1 lead and was tagged for three runs by the Blue Jays who won, 4-3. He faced five batters and didn't get an out as his ERA jumped to 11.37.
"The MRI is showing some stress over the course of the rib where the scapula comes down and bangs into it," head athletic trainer Nick Kenney explained. "So right it's not showing us a fracture on MRI but we're going to get a bone scan to rule that out."
A fracture would mean more serious problems for Holland, a right-hander who has been the Royals' primary eighth-inning set-up man. That spot will now be taken by right-hander Aaron Crow.
Manager Ned Yost said this wasn't Holland's first brush with the ailment.
"It bothered him in Spring Training and kind of went away so last night was the first time that it's bothered him during the season," Yost said. "It didn't bother him when he was pitching, I don't think -- he said it didn't -- but it started to really stiffen up and get sore after he sat on the bench for about 20 minutes. He went into the training room and they decided to MRI it."
Jeffress, in six relief outings for Omaha, has a 2-0 record and a 1.50 ERA. He began the 2011 season with Kansas City but had control problems and was sent to Omaha and then to Double-A Northwest Arkansas. In a total of 71 innings last season, he issued 51 walks but Yost has seen an improvement this year.
"You look at his numbers. He's pitched 12 innings, given up four hits, two runs, six walks. Last year his walks were way up -- they're still a little up but he's got eight strikeouts and he's commanding the ball much better," Yost said. "He's got tremendous stuff, a lot like (Kelvin) Herrera. He's 96 to 99 (mph) with a great breaking ball and he's learning to command his stuff much better. So it's a great opportunity to get him up here and see where he's at."
Dick Kaegel is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.