With left-hander Wei-Yin Chen starting for the Marlins, the Cubs thought it was a good time to rest the left-handed Rizzo as a precaution. Rizzo has battled back stiffness previously in his career.
Willson Contreras, who was called up last week to play catcher, got his first start at first base in place of Rizzo in the Cubs' 4-2 loss. Contreras was converted to catcher from infielder in the minor leagues and had 18 starts at first base in the minors. He homered on the first pitch he saw in the big leagues Sunday, and in 10 plate appearances entering Thursday, he was batting .444 with two homers and five RBIs.
He went 1-for-4 with two strikeouts against the Marlins.
Rizzo is batting .277 with 17 homers and 54 RBIs for the first-place Cubs. He has a commanding lead in voting to be the National League's All-Star representative at first base.
His status is day-to-day.
"I don't think it's anything significant more than stiffness," manager Joe Maddon said.
The Associated Press contributed to this report.