The bad news is that Meister prescribed rest, and Jennings will be placed on the 15-day disabled list by Saturday, Daniels said, when rookie left-hander A.J. Murray will be called up from Triple-A Oklahoma to start against the Athletics in Oakland.
Right-hander Scott Feldman, who threw 69 pitches over four innings in relief of Jennings on Tuesday, will take Jennings' next scheduled start, on Sunday in Oakland.
With three starting pitchers already on the disabled list (Brandon McCarthy, Kason Gabbard and Luis Mendoza), the Rangers will be trying to recover from their 9-18 start using a makeshift rotation of Kevin Millwood, Vicente Padilla, Sidney Ponson, Murray and Feldman. Gabbard is expected to rejoin the rotation May 8 in Seattle if his rehab start this Saturday for Double-A Frisco goes well.
"In the grand scheme of things, at least the problems with Jennings, Gabbard and Mendoza all seem to be short-term issues," Daniels said. "The doctor saw Jason today and said it's nothing specific, just muscle soreness. It's no new injury, just part of the recovery process [from last year's surgery].
"We're going to put him on the DL to give him a little time to let his arm recover. We'll give it time to quiet down, but I don't think he'll be down long."
Jennings, who signed a one-year, $4 million contract as a free agent last winter, has struggled though his first six starts. He is 0-5 with an 8.56 ERA, allowing 27 runs -- 26 earned -- on 35 hits and 18 walks in 27 1/3 innings. Opposing hitters are batting .307 against him this season.
"I'm seeing improvement in his velocity," Rangers manager Ron Washington said. "It's been his location, more than anything. When he gets the ball up, they hit it."
Jennings was relieved the "weird" soreness he described Tuesday night had subsided and that no major injury had occurred.
"It's not as sore today as I thought it would be," he said Wednesday.
A rehab plan and target date for Jennings' return will be drawn up after Wednesday's game. Daniels said it is likely Jennings will not throw for about four or five days, then embark on a rehab plan that will include long-toss sessions and at least one Minor League rehab start. Jennings won't be eligible to rejoin the Rangers before May 15.
Daniels said he didn't expect to put Jennings on the DL until Saturday, unless the club needed another relief pitcher sooner.