He was replaced on defense in the bottom of the inning by catcher Rene Rivera, who has appeared in one other game at first base in his career -- June 2 this season.
San Diego manager Bud Black said the team will know more Friday about Medica's condition. It's also too soon to determine if the team will need to add a player from Triple-A El Paso.
"He's sore," Black said after the Dodgers' 2-1 victory. "We'll know more tomorrow."
Medica entered the night hitting .231 with four home runs and 13 RBIs in 52 games.
First baseman Yonder Alonso is on the disabled list with a tendinitis in his right wrist. Jake Goebbert, a rookie who hit his first big league home run Wednesday in Denver, plays first base.
The Padres have also used catcher Yasmani Grandal at first base in four games this season.
Corey Brock is a reporter for MLB.com. Keep track of @FollowThePadres on Twitter. This story was not subject to the approval of Major League Baseball or its clubs.