"Hopefully it's not a bad oblique," manager Fredi Gonzalez said. "I guess there's different grades of it. We get him back in 15, 20 games. That's a big bat out of the lineup."
The injury came in the 10th inning of Tuesday's 4-3, 19-inning win over the Pirates, when McCann attempted to throw out Neil Walker, who was trying to steal second base. After the throw sailed into center field, McCann grabbed at his lower back. He then met with pitching coach Roger McDowell and the Braves' medical staff, before testing his injury by throwing to the mound.
That's when he left the game, which was tied at 3, and backup catcher David Ross took his place for the remaining eight innings. McCann finished the game 2-for-5.
"It's big, man. It's big. He's our MVP this year so far," Ross said. "I know he has faith in me, and I'm going to hold down the fort as best I can until he gets back. Let him recover, because we're going to need him."
While McCann -- who is hitting .306 this year with 18 homers and 55 RBIs -- is on the disabled list, the Braves will bring up J.C. Boscan from Triple-A Gwinnett.
Boscan is hitting just .194 with no homers and eight RBIs in 53 games this season at Triple-A, but he is on the 40-man roster. However, Ross is expected to receive most of the work behind the plate.
"It's not really a choice. That's why they have me here," Ross said. "They have me here as a backup, as an insurance for Mac. They pay me a lot of money to do that. I welcome the challenge."
Ross is hitting .286 this season with four homers and 16 RBIs.
"We need Mac to get healthy. It's a big, big loss," he said. "There's no way to hide that. He's our MVP right now. He's a candidate for MVP in the National League. There's no way to replace that. I'm just going to try to do the best I can, play my game and try to help this team win."
Chris Cox is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.