McCann said he "tried everything and it just didn't work for me."
"I could swing a bat," McCann said. "I just couldn't swing it and be effective like I wanted to. I still felt I could get a big hit for the team and I was still valuable, so I kept going.
"I feel like sometimes as an athlete you take a couple steps back to go a couple steps forward so I'm looking to coming back better than ever."
McCann said his shoulder already feels better than last season.
"I'm limited right now in what I can do in the gym but I feel amazing," he said. "I feel great.
"My range of motion is better now than it was last season, which kind of shows me it's been there for a while now, I just didn't notice it. It just got worse and worse."
Wren, McCann and five other players, including Uggla and Jason Heyward, spent Wednesday morning at City of Refuge, an Atlanta mission located only a few miles from Turner Field. The players helped serve a meal and visited a daycare for children of clients working at the facility.
The visit was part of the team's series of offseason public appearances through the Southeast.