"I think they're going to back him off for a couple days," Phillies assistant general manager Scott Proefrock said at Bright House Field. "But it was nothing major. The other day, he backed off his long toss. It's nothing big."
Willis is scheduled to pitch Sunday, but that is subject to change.
Right-hander Jose Contreras is scheduled to throw another round of batting practice Friday, and he could see his first Grapefruit League action sometime next week.