Rizzo has been out of workouts for about a week. He said that the issue is similar to what he's experienced before and hopes to avoid being put on the injured list.
The decision to undergo further testing came after a batting practice session on Sunday.
"Once he cooled down, some of that stiffness came back," manager David Ross said Tuesday.
At one point as Rizzo missed time, he was seen hanging out in the bleachers during one Cubs scrimmage. He has a history of minor back issues, which typically have kept him out of the lineup for a few days once every season. He lost considerable weight during baseball's shutdown, but that hasn't helped his back to this point.
Rizzo is in an option year that pays him a prorated $16.5 million salary. The Cubs have an option on him for 2021 as well, at the same price. Despite the back issues over the years, he's averaged 154 games the past five seasons. Last year he missed time with an injured ankle.