The Colts haven't set a timeline for Luck's return.
"The doctors and the trainers have decided to give him a cortisone shot to kind of take away some of that inflammation that's been happening," Ballard said, according to ESPN's Mike Wells.
"He'll continue to rehab. We're just going to shut down the throwing right now to get this thing calmed back down."
Luck is still recovering from shoulder surgery, which he underwent in January. The Colts initially believed he'd be back in time for the start of the season, then placed him on the physically unable to perform (PUP) list when it became evident that he wouldn't be ready to go.
Jacoby Brissett is expected to remain the starter with Luck sidelined.
The absence of their star quarterback has had a profound effect on the Colts, who are mired in the basement of the AFC South.