Baez has been in the Minor Leagues since he lost the second-base job at the end of Spring Training.
He was batting .314 with eight home runs this season for the Iowa Cubs before the injury.
"That's a kick in the butt for the kid, man," Cubs manager Joe Maddon said after Chicago's 6-3 win over Washington on Sunday. "He's been working so hard, he's been doing so well. I don't know the extent of it, but I heard about it, yes."