Right-hander Kyle McPherson will take McDonald's spot in the rotation Wednesday against the Brewers.
"You want your starters to pitch well and as the games count down, we've got to look to give ourselves the best shot that we can have at winning a game," Hurdle said. "Based on James' inconsistency the second half, as I shared with him, when James is right, James is a valuable addition to our ballclub. He's had his challenges the second half."
McDonald has a second-half ERA of 5.84 in his past 12 starts, a stark contrast to a first half in which he went 9-3 with a 2.37 ERA. He admitted after Friday's game he had lost confidence.
McDonald is available out of the bullpen beginning Tuesday. Although he has experience as a reliever while with the Dodgers, he hasn't appeared out of the 'pen since coming to Pittsburgh in 2010. Hurdle said he believes pitching as a reliever will be foreign to McDonald, but is confident McDonald will do his best to help in that role.
"It's going to be up to him what he provides and his buy in. That's what we've encouraged him to do," Hurdle said. "There's still a lot at stake for everybody here and he has a role to play on this club. I anticipate him very good with it from that end."
McPherson, 24, has allowed two runs in 11 2/3 innings of relief for the Pirates since debuting Aug. 20. He was 3-6 with a 3.22 ERA in 12 Minor League starts this season between Double-A Altoona and Triple-A Indianapolis and is the club's No. 10 prospect, according to MLB.com.
Hurdle said the club opted to go with McPherson instead of Jeff Karstens because the veteran righty hasn't pitched in a game since leaving Aug. 31 with right hip flexor discomfort. Karstens is 5-4 with a 3.89 ERA in 15 starts this season.
"McPherson has pitched well and there are many people that speak highly of him through our organization," Hurdle said. "We'd really like to see what he can do. He's got a power arm."