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

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.

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