Rich Hill, 27, the fourth man in the Cubs rotation, is also slated to pitch. Former Cubs right-hander Greg Maddux is scheduled to start for the Padres.
Prior, 26, has not pitched a Cactus League game since March 10, when he threw two innings against Kansas City. Cubs pitching coach Larry Rothschild had Prior throw four innings in a Minor League intrasquad game last Friday to give him a chance to work on his mechanics.
Kerry Wood, sidelined since March 11 with a strained right triceps muscle, had been originally scheduled to pitch as well on Thursday, but he's now been switched to Friday, when the Cubs will play host to the Giants.
There's nothing physically wrong with Wood -- the Cubs just don't think there are enough innings on Thursday for the three pitchers.
"We've got Prior going, and we need Hill to stretch out four, five innings," Cubs manager Lou Piniella said on Wednesday. "I don't know how long Prior is going to go, but assuming he goes three, four innings, then Hill will finish the ballgame."
If Wood, 30, goes one inning on Friday, he could pitch three times next week -- Monday, Wednesday and Friday -- and be ready for the regular season. At least that's how it could happen if Wood doesn't have any setbacks. The right-hander would not get a chance to go on back-to-back days, but he could be given a pass on that.
Wood is adjusting to a new role as a reliever, something he did in 11 games in 2005 before being shut down because of his right shoulder.
"Let's see what happens here over the next few days," Piniella said about Wood. "He's feeling good, and he's ready to go. We just don't have the innings on Thursday. On paper, we don't."
Piniella has preached patience as far as getting Prior and Wood ready for the regular season.
"I don't want to push them to a point where they have any kind of setback, major or minor," Piniella said of the pair. "Let due process take its time. I have to look at myself in the mirror as a manager, and I have to look at the health of these guys first and foremost.
"They'll know and we'll know when they're ready to go," Piniella said. "I don't want to get in the pushing business and all of a sudden [have it backfire]. When they're ready, they'll let us know, and then they can help us."
Carrie Muskat is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.