The right-hander, who made a rehab start for Triple-A Sacramento on Monday, was optioned on Tuesday and thus will continue his stay with the River Cats.
The move came immediately following Oakland's decision to reinstate Cahill from the 15-day disabled list, where he started the season due to a left shoulder stress reaction. Cahill was 1-1 with a 5.95 ERA in six games -- including four starts -- during Spring Training before revealing a neck injury that bothered him late last season.
In his first rehab outing, which came on Monday, Cahill allowed two unearned runs on two hits and three walks in 3 2/3 innings while being monitored on a limit of 60 pitches. Before the transaction news surfaced on Tuesday, Cahill said he'd continue building up his arm strength again by increasing his pitch count in increments of 20.
"I felt good," Cahill said. "I felt a little fatigued after I was done, but I know that's all part of getting my strength back."
The 22-year-old right-hander was very much in the mix for the No. 5 spot in the A's rotation throughout Spring Training until his injury surfaced -- news that played a role in the club's decision to go with lefty Gio Gonzalez.
"I'm happy with the five starters we have right now," manager Bob Geren said as Gonzalez, Tuesday's starter, prepared to take on the visiting Yankees. "This will allow Cahill to raise his game up a bit. He did a nice job for us last year."
Cahill spent the entire 2009 season in the A's starting rotation, posting a 10-13 record with a 4.63 ERA. He joined lefty Brett Anderson in making the jump from Double-A Midland to the big leagues, where he made 32 starts and compiled 178 2/3 innings.
Geren on Tuesday went through a to-do list of improvements Cahill can work on to earn another starting nod in green and gold, chief among them being a better "overall strike percentage."
"That will obviously reduce the number of walks," the A's skipper said. "He'll continue to work on his breaking ball, and if he can combine all those improvements, it won't take him long to get back here."