Rizzo does not have a fracture, according to the Cubs.
The first baseman was removed in the third inning when he rolled his ankle trying to field a bunt by Trevor Williams.
After being tended to by teammates and the medical staff, Rizzo had to be helped off the field.
Depending on the extent of the injury, this could be bad news for a Cubs team trying to secure a berth in the postseason. They entered Sunday with a one-game lead over the Milwaukee Brewers for the National League's second wild-card spot.
Chicago is without star shortstop Javier Baez because of a hairline fracture in his left thumb that is expected to keep him out for at least the rest of the regular season.
In his ninth MLB season, Rizzo has been remarkably consistent and healthy throughout his career. He's missed 10 games in a season just once in the previous six seasons.
Rizzo dealt with a head injury earlier this season but missed only five games. When he's been in the lineup, the three-time All-Star has posted a .289/.402/.516 slash line with 26 homers and 93 RBI.
Cubs manager Joe Maddon put Ian Happ at first base in Rizzo's absence. He also has Victor Caratini available to play the position.