Manager Jim Tracy said Guthrie, a right-hander acquired from Baltimore in the offseason, was pedaling to the ballpark when the chain on his bicycle came off and he tumbled to the ground, jamming his shoulder in the fall.
Guthrie was scratched from his scheduled start Saturday against the New York Mets. He underwent an MRI and there was no sign of structural damage but he is dealing with pain in his AC joint, Tracy said.
Tracy said Guthrie would "miss a couple of starts."
Guthrie, speaking from the Rockies clubhouse late Friday night, said he was pedaling pretty fast when the chain broke off and the bike stopped suddenly, pitching him to the ground.
"It was just kind of a malfunction," he said. "You're riding aggressively at one point and the next thing you know you're on the ground. It's kind of a freak accident for sure."
Guthrie said he fell heavily on his elbow and jammed his shoulder but has been assured that there is no structural damage to the joint.
"At this point, it's pretty much pain. That's what I have. There's no (other) issue," he said. "I have some pain but when that goes away, I can throw, and everything is a go."
Right-hander Guillermo Moscoso was expected to be recalled from Triple-A Colorado Springs to start in Guthrie's place on Saturday.