"There is a certain level of concern with Bartolo you have when he says he's hurt," manager Mike Scioscia said. "Bartolo is a horse. We're hoping this will be short term."
Team physician Lewis Yocum said he did could not even examine Colon because the pitcher was in too much pain, and the club has scheduled their ace for an MRI exam here Wednesday.
Depending on the severity of the injury, Colon may also not be available if the Angels were to advance to the World Series, which begins on Oct. 22, but the club is not looking past the ALCS.
"He is obviously a guy you want on the roster, but we want him to pitch in a game again, too," general manager Bill Stoneman said. "You do what you can and you move forward and you live with it."
The Angels had little time to react to the injury, with rosters due for the ALCS on Tuesday morning. One thought was to add a starting pitcher, but with Jarrod Washburn recovering from strep throat and now able to start Game 2 on Wednesday, the team decided to add Yan, who will bring depth to the bullpen with the ability to provide innings.
Their larger concern, though, was beyond this series and the overall health of Colon, who is signed through 2007. He also suffered from lower back pain over the last month of the season.
"Right now, we are not going to jeopardize what is going to be a long career," Scioscia said.
Colon posted a 21-8 record this season with a 3.48 ERA to lead the AL in wins. The right-hander became the first Angels pitcher to win at least 20 games since Nolan Ryan won 22 in 1974 and could be the first Angel since Dean Chance in 1964 to win a Cy Young Award.
"We had to make a decision quickly," Stoneman said, "but with the information we had this was the only choice. Best-case scenario we would not be in this situation. But it is just too early to tell, and Mike and [pitching coach Bud Black] are not going to run somebody out there who is not able to pitch."
Santana will take Colon's spot in the rotation and likely start Game 4, after John Lackey works Game 3.