Cassevah, who began the season on the disabled list with shoulder inflammation, had previously made five one-inning appearances for Class A Inland Empire -- totaling one run on four hits and two walks -- and debuted at Triple-A Salt Lake on Friday, hurling a scoreless frame despite giving up two hits and a walk.
The sinkerballer has long been eligible to be activated from the disabled list and help the Angels' struggling bullpen, but he still needs more time.
"This is Bobby Cassevah's Spring Training," Dipoto said. "He needs work."
Cassevah, who posted a 2.72 ERA in 30 big league appearances last season, didn't pitch and hardly threw during Spring Training. When he does get activated, he'll likely replace another ground-ball pitcher, rookie reliever David Carpenter.
"He's still working on location," Scioscia said of Cassevah. "The life is back on his fastball, he's got good sink. He just has to refine it."