It was determined after an MRI on Monday that the 30-year-old won't need surgery but will be in a walking boot for five-to-seven days, which puts his regular season in jeopardy with two weeks remaining.
The Cubs have not yet established a timeline for Rizzo's return. He will be re-evaluated following the immobilization period.
"I want to play as soon as possible," Rizzo said, according to Bastian. "Whether it's now or Game 1 of the World Series, I want to play as soon as possible."
Rizzo was helped off the field Sunday after rolling his ankle while attempting to field a bunt.
"Obviously, these weeks in September and October is why I play baseball," Rizzo said. "It's pressure-packed, action-packed. So, to miss any time right now, it sucks. But, it could be worse. I'm grateful it's not worse."
The three-time All-Star is having another strong season, hitting .289/.404/.516 with 26 home runs, 28 doubles, and 93 RBIs.