Scioscia said he didn't know if De La Rosa was getting an MRI and wouldn't specify where the 31-year-old right-hander was ailing.
De La Rosa, coming off a breakout season in which he posted a 2.86 ERA in a team-high 75 appearances, was delayed in Spring Training because of a right forearm strain, averaged 88.3 mph on his fastball when he made his debut on April 12 -- it was 94.6 mph last year -- then went on the disabled list again with irritation in his right s/c joint.
De La Rosa worked his way back up to a rehab assignment, was appearing every other day at Triple-A from May 4 to last Friday and looked primed to join the Angels in Toronto last weekend. But he gave up a couple of runs in 1 1/3 innings in his most recent outing, and though he finished it, he hasn't shown enough progress.
"He hasn't quite moved forward at the pace that he can," Scioscia said. "Maybe it's just a matter of catching his breath. He'll be evaluated, and we'll see what next the step is."
Alden Gonzalez is a reporter for MLB.com. Read his blog, Gonzo and "The Show", and follow him on Twitter @Alden_Gonzalez. This story was not subject to the approval of Major League Baseball or its clubs.