Baek had allowed one run in two innings in Sunday's 8-6 loss to the San Francisco Giants at PETCO Park when he was removed from the game as a precaution when he complained of feeling a "sharp pain."
Baek said he felt better Monday an hour before the Padres opened a three-game series at Coors Field against the Rockies, although that was before he attempted to test his triceps.
"He's better, but still a little sore," Padres manager Bud Black said of Baek, who is 5-10 with a 5.06 ERA this season. "We're going to evaluate him day-to-day."
Baek said Sunday and reiterated again Monday that he doesn't think he will miss his next start Sunday on the road against the Washington Nationals.
Since the Padres are currently employing a six-man rotation and the team has Thursday off, Baek would be pitching on six days' rest.
San Diego general manager Kevin Towers has said that he likes Baek, and that the right-hander could well figure into the Padres' plans for next season, possibly as a pitcher to help to fill out the back end of the rotation.
In his previous start before Sunday, Baek allowed three hits over seven scoreless innings in a victory over the Los Angeles Dodgers on Sept. 8.
In other injury news, the status of center fielder Jody Gerut (sprained left middle finger) hasn't changed. Gerut hasn't started a game in center field since Aug. 27.
Another outfielder, Chip Ambres, who strained his left knee Friday, took batting practice before Monday's game and said he could return in the next "two or three days."
Corey Brock is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.