"It's certainly been difficult," Dipoto said.
At the moment, five members of the Angels' Opening Day bullpen are unavailable as relievers. Jerome Williams is expected to start on Wednesday, with Tommy Hanson on the bereavement list. Garrett Richards is already taking the rotation spot of Jered Weaver (broken left elbow). Kevin Jepsen has been on the disabled list since April 13 because of a right shoulder strain and isn't expected to pick up a baseball for at least another week. Mark Lowe has been out since Saturday with a neck strain and won't be eligible to be activated until May 5.
And now Burnett is out, though the Angels don't expect him to have to go on the DL.
"It's just part of the process of coming back from the spurs probably," Burnett said of his forearm tightness. "I got more range of motion [after offseason surgery to remove bone spurs] and was able to do more with the ball than I had in the last probably year or two. It's just part of the process, I guess. I'm going to try to be careful early on, not have that drag on and be feeling it in July and stuff."
Burnett said his forearm felt "pretty good" when he last appeared in a game on Sunday, throwing a scoreless eighth inning in an eventual walk-off win against the Tigers. The tightness, he said "is just something I've been dealing with off and on for the last two weeks; has its good days and bad days."
Burnett's absence leaves closer Ernesto Frieri and sage lefty Scott Downs as the only experienced, reliable members remaining in the Angels' bullpen. Dipoto said the new guys, particularly De La Rosa and Roth, have done "Yeoman's work" filling in. But given their experience and track record, they can only do so much.
"As much as the individual contributions can be good, it's difficult," said Dipoto, whose team doesn't have another off-day until May 6. "You're trying to navigate through winning games, and generally speaking, you'd like to give guys a chance to cut their teeth and they're getting thrown in the fire."
Alden Gonzalez is a reporter for MLB.com. Read his blog, Gonzo and "The Show", and follow him on Twitter @Alden_Gonzalez. William Boor is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.