CHICAGO -- The Cubs lost another starting pitcher Tuesday as Matt Garza went on the disabled list, but they got good news on Andrew Cashner and expect Randy Wells back this weekend in the rotation.

Garza was placed on the 15-day disabled list, retroactive to May 18, with a right elbow bone contusion.

"I'm not happy going on the DL," Garza said. "I'd rather get healthy and come back in a start or two and get after it."

It wasn't a specific pitch that caused the problem, Garza said, but something that's been nagging him for some time. He underwent an MRI on Monday, which showed there was no structural damage.

"We're just happy it's just a bruise," Garza said. "It could've been worse. There's a lot of reasons things like that happen. It's more wear and tear. If you're a runner and your knees are sore, it's usually a bruise. It's something that happens."

If all goes well, Garza (2-4, 3.72 ERA) could be ready for the Cubs' series in St. Louis, which starts June 3. He will not throw for a few days to give the bruise time to heal.

"Optimistically, we feel that as soon as the full range of motion is back and he gets rid of the discomfort, he could be ready to pitch in St. Louis," Cubs general manager Jim Hendry said.

The Cubs have been scrambling to fill two spots in the rotation with the loss of Cashner and Wells after their first turn in the rotation. They can't afford to lose Garza for long.

"It was the best news we could hope for," Hendry said of the MRI results.

Cashner has been on the disabled list since April 6 with a strained right rotator cuff and was examined on Monday by orthopedic specialist Dr. Lewis Yocum, who confirmed what the Cubs team doctor reported, which was aggravation of the shoulder. Cashner felt some discomfort before he was to pitch in a game at extended spring camp in Mesa, Ariz., last week.

"No surgery is needed or even close to being needed," Hendry said of Cashner, who will restart his rehab.

Yocum was unable to provide an explanation as to why Cashner aggravated the shoulder but felt the right-hander will heal fine.

Wells, on the disabled list since April 5 with a strained right forearm, pitched four innings in his second rehab start Sunday with Triple-A Iowa. He was back at Wrigley Field on Tuesday and will start Saturday in the second game of the Cubs' series against the Pirates.

"He threw the ball with a lot of snap, a lot of velocity," Hendry said of Wells' last rehab start. "He wasn't sharp but the arm strength was good and the slider was good, and he'll be ready to go Saturday."

Wells said he was ready to throw 90 pitches. Being sidelined has been "difficult," he said.

"You start asking a lot more questions and you start paying a lot more attention to minor things [when you're hurt]," he said.