Upton sat out practice on Friday after he was seen limping after a batting practice session on Thursday. On Friday, Upton underwent treatment before being sent to have an X-ray and MRI.
Upton, 30, was found to have sesamoiditis, or inflammation in the bone behind the ball of the foot. According to the team, he will be in a cast for two weeks, before switching to a walking boot for four to six weeks.
"[The discomfort] is more in the toe area, but we're calling it a foot [injury]," said Braves manager Fredi Gonzalez on Friday.
Atlanta said the centerfielder would be likely be able to begin baseball activities again in April. Todd Cunningham and Eury Perez are currently behind him at centerfield on the team's depth chart.
Upton signed a five-year, $72.25 million contract two seasons ago when he joined the Braves. In two years in Atlanta, he has a .196 batting average with a .278 on-base percentage, a .311 slugging percentage, 61 RBI, 21 home runs and 324 strikeouts.
In 10 MLB seasons with the Rays and Braves, Upton has hit .243 with 139 home runs and 508 RBI.