The Philadelphia Phillies demoted rookie right-hander Mick Abel, who has struggled since he struck out nine in his major league debut, to Triple-A Lehigh Valley.

Abel pitched six innings of five-hit ball with nine strikeouts and zero earned runs in his debut May 18 against the Pittsburgh Pirates. He was sent back down to the minors shortly after because of the nature of the spot-start, but he returned in early June and wasn't the same pitcher.

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