McCann was visibly upset to be out of manager Fredi Gonzalez's lineup Saturday night for the second straight day.
"I'd like to be playing," McCann said.
McCann said Gonzalez "feels otherwise, which is his decision."
Gonzalez said McCann is "fine" and will start on Sunday.
McCann said a recent MRI showed the problems. He had a cortisone shot in the shoulder last week.
"I've got a cyst sitting on a joint," McCann said. "I've got a frayed labrum. Yeah, I've got those things going on in there.
"I'm going to manage it and get through the season and then see what we need to do."
Added McCann: "I can play. I can do all the things I need to do to play."
David Ross is starting on Saturday night against the Dodgers for the second straight game.
McCann, a career .280 hitter and six-time All-Star, is hitting only .229 but he has 18 homers and 57 RBIs. He is hitting only .111 (4 for 36) in August.
Ross is hitting .272 with six homers and 14 RBIs.