"We feel like we're putting him in danger if we throw him out there and have him pitch tomorrow," Phillies general manager Ruben Amaro Jr. said. "We're just trying to be proactive about it, so he doesn't make it any worse than it already is."
Phillies right-hander Kyle Kendrick will take Oswalt's place in the rotation and pitch Saturday against the Braves. Right-hander Scott Mathieson will take Oswalt's place on the 25-man roster. He was recalled after Friday's game. Kendrick threw 46 pitches in three innings Sunday in a 14-inning loss to the Mets. Kendrick said he hopes to pitch at least five innings Saturday. Phillies manager Charlie Manuel estimated Kendrick could throw 65 to 70 pitches.
The Phillies can backdate Oswalt's DL stint 10 days, which would make him eligible to start next Friday in Atlanta.
Oswalt, who felt some discomfort following a bullpen session Thursday, is not sure if he will be ready to be activated.
"My biggest thing is I don't want to go out there and not be 100 percent," Oswalt said. "I don't want to go out and throw three, four innings and they have to come get me. We may have to test it out before then in a game somewhere just to see where I'm at."
That could mean a few innings in a rehab appearance.
"It hasn't really gotten any better," Oswalt said. "I could probably pitch Saturday, but I couldn't promise anything on results. We'll give it a few more days to see how it feels, and maybe throw Sunday or Monday on the side and see where I'm at and kind of go from there."
Oswalt left the team following his April 26 start in Arizona to be with his family in Mississippi. Tornadoes tore through the state and caused damage to his home and the home of his in-laws. Oswalt spent eight days in Mississippi, spending hours sitting in his excavator clearing trees on the road to his home.
"That probably doesn't help very much, but he was taking care of the things he needed to take care of," Amaro said.
Oswalt said he hoped the time away from baseball activities might help his back, but it did not. He said his work clearing trees did not hurt him.
"I'm sitting in this chair," he said, sitting in front of a locker inside the Phillies' clubhouse. "You're not really moving your body. ... It bothers me when I really crank down on it. I can go out and play catch and feel pretty good. When I start letting it go, it's kind of stiff."