"I'm going to try and give myself a little time and let it rest," Grabow said. "I'm going to work on some things and get freshened up and help later on."
Grabow has struggled out of the bullpen. He already has lost his primary setup role and had been relegated to mopup duty, despite being in the first year of a two-year, $7.5 million deal.
"It is a sprained left knee," Grabow reported. "The same thing as before. I'm just going to let it calm down and get it right and obviously I'm not pitching the way I should be pitching and I want to get it right."
The Cubs selected the contract of right-hander Andrew Cashner from Triple-A Iowa.
"We DL'ed Grabow," manager Lou Piniella explained. "He's got the inflammation in the knee and he'll get a chance when he's OK to work with pitching coach Larry Rothschild a little bit and hopefully he can get going. We need for him to pitch better. He's been getting the ball up and he's been getting hit."