Colvin was the runner on third base when he was struck in the upper left chest by a piece of teammate Welington Castillo's broken maple bat. A Cubs spokesman said Colvin was conscious and stable, but that his chest wall had been punctured. Colvin will be hospitalized for at least a few days, and he was being treated to prevent against a potential collapsed lung.
The rookie won't play again this season, the Cubs announced.
Colvin scored on the play before anyone else realized the extent of the injury.
"I feel really bad about it," Castillo said. "It wasn't on purpose, but he's my teammate. I hope he's getting better."
Maple bats have long had a reputation for exploding and sending out potentially damaging shards.
"These bats, I'm amazed it doesn't happen more," manager Mike Quade said.
Teammate Jeff Baker said he refuses to use maple bats for fear of an incident like Sunday's.
"I don't want that on my conscience," he said.
Colvin finishes the season with a .254 average, a .316 on-base percentage and 56 RBI in 135 games. He and Florida's Mike Stanton both have 20 homers, tied for the lead among major league rookies.
Colvin remained in stable condition at Jackson Memorial Hospital in Miami Monday and is expected to stay in the hospital a few more days for observation.
He released a statement Monday:
"I want to thank Cubs fans for their support all season, especially right now, and let everyone know that I'm doing OK," said Colvin. "I also want to thank everyone who has helped take care of me here in Miami – the Cubs and Marlins training and medical staffs, the EMTs at the ballpark and everyone here at the hospital.
"You never want to have a season end early, and I'm disappointed that I'm not going to be able to make it through the finish line with the rest of my teammates. That being said, I couldn't be more thankful for the Cubs organization, my teammates and the opportunity to play for Cubs fans my rookie season. Thank you from the bottom of my heart."
Update: Colvin Says He's Doing Well
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