Chatwood left a 3-0 loss to Cincinnati on Monday night after pitching only four innings because of pain in the muscle when he threw his fastball. He flew to Denver on Tuesday and had a medical examination that left the Rockies optimistic there's no serious damage.
He was scheduled for an MRI later in the day that would give the Rockies a better idea of how long he might be out.
"The initial reports sound pretty good," manager Walt Weiss said. "We'll wait to hear what comes back from the MRI."
Chatwood said he'd never felt pain in his triceps until his start on Monday night. He first felt it on a pitch to Shin-Soo Choo in the third inning. It bothered the right-hander whenever he threw his fastball. Weiss took him out in the fifth as a precaution after Chatwood had thrown 64 pitches, giving up one run and four hits.
Weiss said Chatwood likely would miss his next scheduled start on Saturday even if the MRI results bring good news.
"I don't want to commit to that right now," Weiss said. "It would probably be tough to make his next start."
The Rockies put closer Rafael Betancourt on the 15-day disabled list last weekend with a strained groin.