The 25-year-old, who had surgery to remove bone spurs last October, was held over in Extended Spring Training until mid-May, then made three starts at Class Low-A Peoria and one at Daytona before returning to Arizona.
An All-Star at Double-A a season ago, Shaver won seven games and posted a 2.99 ERA while logging 150-plus innings. He is scheduled to have his shoulder scoped Friday and is likely to miss the remainder of the season.
"I'll be out here for a good little while," Shaver said from Mesa, Ariz., this past weekend. "I'm definitely done for the season at this point."
Shaver was 1-0 with a 2.49 ERA in 18 1/3 innings combined this season. He was the Cubs' fourth-round draft pick out of William and Mary in 2004.
Elsewhere, right-hander Michael Cooper hadn't pitched since mid-April following his own bout of shoulder discomfort, and won't any time soon.
A 26th-round Cubs draft pick from California a season ago, the 23-year-old Cooper underwent shoulder surgery in Chicago last Friday to repair his rotator cuff and will likewise miss the remainder of 2007.
Cooper was 0-2 with a 2.70 ERA in just three appearances spanning 3 1/3 innings with Daytona (Class High-A) this season.
"All throughout Spring Training, I felt great," said Cooper. "I threw my first two innings in Daytona and still felt great. Then after my second outing, it started to flare up. By the third outing, I had to come out of the game."
Cooper spent his only other season with the Cubs last summer in Boise, where he was 2-0 with a 1.23 ERA in 22 innings. He finished 18 games and recorded nine saves in 19 appearances.
"With the way things are going (in Chicago) this year, it's a good time to be playing," Cooper said. "I guess I'll wait until next year to give it a shot."