The results of the MRI won't be known until later Monday, though manager Bud Black said there's some "biceps involvement," in addition to damage to the shoulder.
"When he landed, it jarred the shoulder and did damage to the biceps tendon," Black said.
Maybin won't return to the Padres' complex in Peoria until Wednesday at the earliest, as he's headed to North Carolina because of a death in the family.
Maybin robbed the Dodgers' Juan Uribe of extra bases in the fourth inning, racing from center to right for the catch. But between pitches to the next batter, Maybin dropped his glove and was in obvious pain.
The injury came a day after Maybin hit his first home run of the spring.
"Man, it felt good," Maybin said after his home run on Saturday against the Royals. "I know it's only two games in, but it felt really good to kind of click one. Just to kind of get that reassurance that the body feels well. You always gain confidence when you're able to put together a good at-bat."
Last season, Maybin spent time on the disabled list with an impingement to his right wrist, which later required season-ending surgery. Maybin also missed time after he tore the posterior cruciate ligament in his left knee.
Maybin hit .264 with nine home runs and 40 steals in his first season with the Padres in 2011. He then hit .243 the following season.
Will Venable is the likely candidate to see time in center field, as he did a year ago, when he appeared in 80 games there.
The Padres also have Carlos Quentin, newcomer Seth Smith and Chris Denorfia slated to see plenty of playing time in the outfield, though all are corner outfielders.
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.