CHICAGO — Chicago Cubs ace Carlos Zambrano was scratched from his scheduled start Sunday against the Philadelphia Phillies to give him extra rest because of a tired arm.

Sean Marshall started the finale of a four-game series against the Phillies at Wrigley Field.

Zambrano, a 13-game winner this season, is 1-1 over his last five starts, twice failed to get out of the fifth inning and has seen a drop-off in his velocity.

Zambrano had a tired arm during the same period a year ago, going winless during August. He bounced back to win four of his starts in September as the Cubs captured the NL Central.

Zambrano's next start could come Tuesday or Wednesday at home against the Houston Astros.