Manager Charlie Manuel preferred to call it a strained rib cage.
"That would be the old time diagnosis," he said after the 10-3 loss to the Rockies.
The Phillies said Ruiz is day-to-day, and they will know more Saturday if he will be able to play. Triple-A Lehigh Valley catcher Lou Marson was scratched from the lineup about 15 minutes before Friday night's game against Scranton/Wilkes-Barre. He will be in Denver on Saturday as a precaution in case Ruiz can't play and needs to be placed on the disabled list.
Ruiz, who was in the trainer's room long after the game, was unavailable for comment.
"It's hard for you to breathe," Manuel said of the injury. "It'll keep tearing if you keep playing."
Ruiz apparently strained his oblique when he caught a popup in foul territory in the third inning.
Chris Coste took Ruiz's place in the seventh.
Todd Zolecki is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.