"When he came in today [Friday] he tried to swing," manager Joe Maddon said. "It still didn't feel right. As opposed to continually waiting, we just want to find out what we're dealing with."
Baez will miss his fourth consecutive game Friday and will miss Saturday's contest against the Milwaukee Brewers as well. He was a late scratch Thursday after attempting to take batting practice.
The Cubs won't have a timetable for him until after they see the results of the MRI.
Meanwhile, pitcher Yu Darvish was cleared to start his game Saturday after missing his previous outing with tightness in his right forearm. Darvish said he's been dealing with the injury for over two months, having first felt something during a game July 3. It hasn't affected his performance, as the right-hander has compiled a 2.93 ERA in nine starts since that appearance, but it might have limited some outings.
"Every time in the fifth or sixth inning, I start feeling tightness," Darvish said. "That's why Joe [Maddon] sometimes pulls me."
Yu Darvish discusses forearm issue
Watch Yu Darvish discuss the forearm issue that forced him to miss a start. He says he's fine for Saturday's outing against Milwaukee.
"We were pleased with what we saw on the MRI," Kimbrel said. "Take a few days off, let it rest and crank it back up."
Kimbrel isn't sure if his June signing with the Cubs has led to the two different injured-list stints for him, including one for a sore knee.
"We'll never know," the right-hander said. "I've been pitching in the big leagues for a few years. You don't go through a season without ups and downs."
Kimbrel is available to come off the injured list Thursday.