Carpenter informed the players' union of his decision Friday, and the Cardinals received confirmation through Major League Baseball that Carpenter has been removed from Team USA's roster.
"There's nothing saying that I need to be ready for the season right now, and for me to put myself in a situation where I need to ramp it up before the Classic just wasn't a smart idea," Carpenter said. "I'm super-disappointed, but I'm at peace with it just because I know it's the right thing. I could have gone and played, but I'm in a situation now where I feel like I'm teetering on overdoing it."
The plan is for Carpenter to take the weekend off from batting practice and to remain out of spring training games at least until Friday.
It would have been Carpenter's first WBC. He was penciled in as a utility player for the squad, which opens the tournament on March 10 against the Dominican Republic. He was set to join the team in Fort Myers, Florida, after Monday's game.
Carpenter was scratched from the Cardinals' spring training game Thursday and has not played since. He took batting practice Friday, and Cardinals manager Mike Matheny said he was sore enough afterward to decide to forgo the tournament.
Matheny said it would "be a little while" before Carpenter is back in game action for the Cardinals, but at this point the team is hopeful he will be ready by Opening Day on April 2 against the Chicago Cubs.
"He was concerned enough that he's backed off swinging," Matheny said. "He hit enough yesterday to know it wasn't how he wanted it to feel."
Carpenter, who led the Cardinals with an .885 OPS in 2016, missed about three weeks last season with a strained oblique muscle in his right side. He previously played second and third base, but the Cardinals have decided he will be their everyday first baseman after they let Brandon Moss and Matt Holliday leave via free agency.
"He was extremely excited about the opportunity [to play in the WBC]," Matheny said. "He wasn't happy [about the injury]. The honor, the privilege, the experience, all of that is something that I know meant a lot to him. I'm disappointed for him."
Also pulling out of the WBC on Saturday was Miami Marlins catcher A.J. Ellis, who is dealing with a hamstring injury. Ellis was slated to be one of three catchers for Team USA, along with Buster Posey and Jonathan Lucroy.
Marlins manager Don Mattingly said he expects Ellis to be out another 10 to 12 days "before he gets back out there."
"He's definitely disappointed," Mattingly said. "I know he wanted to be part of this. He knows it's really his last shot to be part of this. So he's disappointed. But A.J. is the kind of guy who knew he didn't want to go there and get hurt more and not be ready for the season."
Mattingly said the Marlins are "not that concerned" about Ellis being healthy by Opening Day in four weeks but felt a need to "be cautious."
Information from ESPN's Jayson Stark was used in this report.