Pineiro was supposed to throw about 90 pitches, but left a minor league game against the Chicago Cubs' Triple-A team after just two innings and 35 pitches.
Angels manager Mike Scioscia told reporters in Arizona that Pineiro still might have time to avoid the disabled list, but that he might be held back from his first scheduled start, April 5 against the Tampa Bay Rays.
"I want to get a better understanding, but I guess he just felt a little stiffness," Scioscia said, according to the Orange County Register.
Pineiro strained an oblique muscle warming up on July 28 last year and missed seven weeks. In his first season with the Angels, he went 10-7 with a 3.84 ERA last year.
If he starts the season on the disabled list, the Angels have limited options in the fifth-starter spot. Longtime minor leaguer Matt Palmer is an option, but he has had a rough spring. He allowed six runs and 10 hits in four innings of the Angels' 6-6 tie with the Colorado Rockies. They could also use reliever Hisanori Takahashi in the rotation, but that would leave them without a left-hander in the bullpen to start the season.
Mark Saxon covers the Angels for ESPNLosAngeles.com.