Carpenter had to exit the game in the first inning, after doubling into the left-field corner off Padres starter Edinson Volquez.
Carpenter said he felt "something funny" in his right side as he finished his swing and continued having discomfort as he ran the bases. Carpenter grabbed his side as he neared second and was then quickly met by manager Mike Matheny and a trainer.
After the brief consultation, Carpenter left the field.
"I got to second and knew something wasn't right, but I didn't know what it was," Carpenter said. "It scares you more than anything. As the night went on, it got gradually better."
Carpenter will undergo an MRI exam on Wednesday to determine whether there was any tear to his oblique muscle. If not, he may be able to avoid joining six other teammates on the disabled list.
"There's something going on there, but it might not be to the extent that we thought," Matheny said. "Hopefully, what the trainers are seeing right now is something we can get in front of."
Carpenter was also not exhibiting signs of an oblique strain -- like hurting when breathing or laughing -- in the hours after coming out of the game.
Matheny has become frustratingly familiar with seeing his players exit the field injured. Since putting Jon Jay on the disabled list on May 16, Allen Craig (left hamstring strain), Kyle McClellan (right elbow strain) and Lance Berkman (torn right knee meniscus) have all left games in progress due to injury. Those three have since joined Jay on the DL.
Daniel Descalso replaced Carpenter as a pinch-runner and remained in the game to play third base. Carpenter was starting at third in place of David Freese, who is getting days off as he works to correct his swing. Carpenter leads all National League rookies with 20 RBIs and is batting .288 this season.
Jenifer Langosch is a reporter for MLB.com. Read her blog, By Gosh, It's Langosch, and follow her on Twitter @LangoschMLB. This story was not subject to the approval of Major League Baseball or its clubs.