Padilla, healed from an irritated nerve in his forearm, failed a pregame test when he was unable to pitch because of a recurring bulging disk in his neck.
Padilla said it is the same problem that limited him last year to one start after Aug. 16.
"I worked very hard to come back, and this is the result," said Padilla. "I felt my neck a little bit tight in my last rehab game [Wednesday], but I never imagined it would be this bad."
Garland, who pitched six innings Wednesday night in the Dodgers' 3-0 loss to Colorado in Los Angeles, complained during the game and did not accompany the club on the trip east.
Manager Don Mattingly said the back of Garland's shoulder has bothered him at least the past two starts. He underwent an MRI that showed no considerable change from the one taken during the offseason when he was signed to a one-year contract plus an option for 2012. Mattingly was vague about the timetable for Garland's return.
"His recovery is based on how he feels," Mattingly said. "It sounds like his shoulder was killing him, but he had been doing his normal throwing. Jon knows his body. He knows exactly how to take care of himself."
Garland is 1-5 with a 4.33 ERA and a four-decision losing streak, the lone win coming on April 20. He has 28 strikeouts and 20 walks in 54 innings.
He was signed to be a workhorse, having gone 10 seasons without a disabling injury. But in keeping with the Dodgers' injury-prone ways this year, Garland has been sidelined twice, the first being a strained oblique muscle he suffered in Spring Training.
The injuries will be costly for Garland. He receives a $3.5 million base salary this year with a $1 million signing bonus, but there are another $3.525 million in incentives this season if he pitches between 150-190 innings, plus an $8 million option for next year that would vest at 190 innings.
Padilla has been out since May 14 with irritation of the right radial nerve. He started the season on the disabled list after undergoing surgery in February to free that entrapped nerve.
De La Rosa, who has allowed one earned run in five big league innings, was 2-2 with a 2.93 in eight starts at Double-A Chattanooga before he was promoted to the Dodgers on May 24.