McDonald, who has started each of Atlanta's first five games and leads the team with 3.8 assists per game, suffered the injury in Friday's 92-87 loss to the Las Vegas Aces. The team announced the injury on Tuesday.
Rookie Haley Jones could take on a bigger role to help the Dream adjust to losing McDonald.
McDonald is averaging 6.0 points per game.
McDonald, the No. 3 overall pick in the 2021 WNBA draft from Arizona, is in her third season.