"I just know it's something that doesn't feel right," Napoli said. "We're going to see what it is."
Catcher Ryan Budde was recalled from Triple-A Salt Lake to fill Napoli's roster spot. Budde appeared in 12 games for the Angels last season, delivering several quality defensive performances lauded by manager Mike Scioscia while batting .167 in 18 at-bats.
Napoli said the shoulder has been bothering him "for a while," adding, "I've had good days and bad days. On the days I feel good, I try to take care of it. Other days it hurts every time I throw it back to the pitcher."
Napoli is second on the club with 12 homers, despite having only 142 at-bats while sharing the job with Jeff Mathis, who drove in three runs with a pair of hits and guided Jon Garland through a complete-game, 7-1 victory over the Blue Jays on Sunday.
Napoli is batting .204 with 29 RBIs in 47 games, while Mathis is hitting .220 with five homers and 23 RBIs in 46 games.
Bobby Wilson, hitting .310 at Salt Lake in 52 games, fractured his right thumb on Saturday and was placed on the DL. Budde is hitting .200 in 37 games. Tim Duff was promoted from Double-A Arkansas to fill the void at Salt Lake.
Lyle Spencer is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.