Lester was pulled in the second inning of Thursday afternoon's game against the Cincinnati Reds due to the injury and saw a team doctor after the game. He allowed nine runs (seven earned) in 1 2/3 innings as the Reds outlasted the Chicago Cubs 13-10.
"There's no minimum or maximum, just that it's a 10-day stay and then we'll figure it out," Cubs manager Joe Maddon told reporters Friday of Lester's return.
Lester was replaced by left-hander Mike Montgomery in Thursday's game after facing 11 batters in the second inning and Cincinnati leading 8-0. Montgomery will take Lester's slot in the rotation.
The 33-year-old Lester is 8-7 with a 4.37 ERA over 148 1/3 innings in 26 starts this season after helping the Cubs win the World Series last year. He signed a six-year, $155 million deal before the 2015 season.
Montgomery is 3-6 with a 3.64 ERA over 96 1/3 innings in 35 games this year, including eight starts.
The Cubs also placed right-handed reliever Justin Grimm on the DL with a finger infection. Grimm was credited with the loss in Thursday's game against the Reds. In an inning of work, he allowed two runs on a hit and two walks, while striking out two.
Grimm is 1-2 with a 5.40 ERA over 43 1/3 innings in 39 relief appearances this season.
In corresponding moves, the Cubs called up right-hander Felix Pena and left-hander Rob Zastryzny from Triple-A Iowa.
Pena has a 4.50 ERA in 16 innings across 10 appearances this year. Zastryzny has one appearance for the Cubs this season, allowing three earned runs in four innings.