The Phillies have demoted rookie right-hander Mick Abel, who has struggled since he struck out nine in his major league debut, to Triple-A Lehigh Valley and returned Taijuan Walker to the rotation.

The move is intended to give Abel a chance to reset, manager Rob Thomson said. Seth Johnson will take his spot on the roster.

Walker will start Tuesday at San Francisco. He could pitch four innings or so. Then, during the All-Star break, the Phillies will reassess.