I really think that Caleb has been playing with a less than fully healthy back all season, especially since his back has been an issue in prior seasons.
Even if his back is only slightly stiff or sore during a game (which will usually become worse during the course of a game due to the repeated pounding and trauma to the injured area), it can negatively affect his mobility, shooting mechanism and accuracy, and other aspects of his game. If he comes back too soon, all the medications in the world won't allow him to play at his maximum level during a game, and his next recovery could take even longer. And basketball is a sport that can cause significant trauma to a back injury and joints in general..
Trust me, I know from experience (horrible and dumb decision to insist on playing again before a back injury was fully healed after muscle and ligament damage), although I realize that all back issues aren't identical. And if Caleb was going to redshirt a few seasons ago because of his back, then the injury seems to have been a chronic one that could periodically flare up again with additional stress or trauma to the area.