Bryce Harper, who has not appeared in Grapefruit League play since Thursday, was set to miss the Phillies' games again on Monday, a split-squad day against the Pirates and Yankees.
Harper is dealing with back stiffness and the Phillies are playing it safe.
"He's been doing a lot of work, a lot of swings, a lot of defensive work," Thomson told reporters. "He got a little stiff, so we're just being precautious. We'll just back him off for a few days."
Stay in the game with the latest updates on your beloved Philadelphia sports teams! Sign up here for our All Access Daily newsletter.
Harper has been busy at camp, working out early in the morning at first base on the half field at BayCare BallPark with infield coach Bobby Dickerson and starting nine of their 14 games from Feb. 28 through March 14.
Harper last season missed the Phillies' first 30 games recovering from Tommy John surgery but avoided the injured list thereafter. He started 125 of 132 games. Some of the only time he missed came on on Aug. 10-11 when he felt back spasms and exited against the Nationals after his second plate appearance, then missed a game the next day.
Getting Harper back to or as close to 100 percent as possible for Opening Day is the priority. The Phillies finish up in Florida next Monday and open the season against Atlanta at home next Thursday. They expect to have him back in the lineup later this week.