Morneau, who underwent surgery on his neck on June 29 and missed the second half of last season with a concussion, is expected to resume working out on Wednesday if he feels better.
"Morneau will be backed off a couple of days and is seeing some doctors," Gardenhire said. "He has migraine headaches. It has nothing to do with his concussion, and it has nothing to do with his neck. It's just migraine headaches, so they're giving him medicine."
Morneau has been working out in recent weeks but has yet to swing a bat, which is the next step in his recovery from the surgery that removed a herniated disk fragment in his neck.