Manager Bud Black said before Saturday night's game against the Colorado Rockies that right-handed reliever Donn Roach would step into the rotation to fill Cashner's spot on Sunday.
''(Cashner) just informed me that he was sore, and as much as he hated to do it, it might be a time for him to take a step back to take two forward,'' Black said. ''And I totally agreed that it was a prudent decision.''
The Padres also recalled right-handed pitcher Kevin Quackenbush from Triple-A El Paso to fill Cashner's roster spot.
Cashner last pitched on Tuesday at Cincinnati. He said he felt soreness in his elbow when he threw a side session on Thursday and spoke to Black about the issue on Friday after the team arrived in Denver for a three-game series.
''It's one of the toughest decisions I've had to make,'' Cashner said. ''I've been doing well. I think it's just kind of my elbow has been a little sore and it's gotten better and then it kind of took a step back after Cincinnati.
''So, just from a recovery standpoint, I haven't recovered as fast. I think it's smarter right now to err on the side of caution. I think I've just got some inflammation in there and hopefully I won't be on the DL longer than 15 days.''
The Padres return to San Diego on Sunday night and Cashner is scheduled to have an MRI and be examined by team doctors on Monday.
Well aware of the recent rash of elbow ligament injuries in baseball, Cashner expressed some concern about the seriousness of his injury but remains optimistic that it nothing beyond some inflammation in the joint.
''It's kind of crazy not to think about it because it's definitely out there,'' Cashner said.
''But I just think it's kind of coincidence. Pitching in the big leagues has gotten tougher. Hitters are better. Guys are throwing harder. It's just a lot more stress you're putting on your arm, but I'm not worried about my ligament at all. I don't think it's that. But I go for an MRI on Monday and we'll know more then.''