Manager Dave Roberts scratched Betts from the lineup for the second consecutive game Saturday but said previously that he didn't expect the injury to be serious and that the star center fielder was in line for an MRI.
Both Roberts and Betts were optimistic Sunday that the former MVP would only be sidelined for approximately two weeks.
Roberts was not sure yet whether the injury is a hairline fracture or a larger break, but the loss will be significant regardless. Betts is batting .273 this season with 17 home runs, 40 RBIs and 6 stolen bases for a team that is battling for first place in the National League West with the San Diego Padres.
"You're taking one of the best players in baseball out of the lineup," Roberts said. "It's a big blow, but at least we know what we're dealing with and we're going to get him back sooner rather than later."
Betts was injured during the first inning of Wednesday night's game against the Los Angeles Angels when he collided with Cody Bellinger in the outfield on a fly ball. Betts played the rest of that game. "A week from now, we'll know more," Roberts added.
In other moves Sunday, the Dodgers activated left-hander Andrew Heaney, who will start the series finale against the Guardians, recalled outfielder Zach McKinstry from Triple-A Oklahoma City and optioned right-hander Reyes Moronta back to Triple-A.
The Associated Press contributed to this report.