According to Gordon Wittenmyer of the Chicago Sun-Times, Baez is "unlikely" to play in September after suffering a fractured thumb. Wittenmyer noted a specialist confirmed the injury but discovered there was no ligament damage.
The hope is he can play in October should the Cubs advance to the playoffs.
Baez, 26, is slashing .281/.316/.532 with 29 home runs and 85 RBI in 133 games this season. He was also Chicago's best player last year when he slashed .290/.326/.554 with 34 home runs and 111 RBI as a National League MVP candidate who helped carry the team into the playoffs.
Addison Russell would typically be the next shortstop with Baez sidelined, but he is under concussion protocol, per Zach Zaidman of the Cubs Radio Network. That leaves highly regarded prospect Nico Hoerner, who is in the starting lineup for Monday's game against the San Diego Padres.