Rodriguez pitched two scoreless innings of relief for the Dodgers Sunday after being recalled to replace Paul Maholm, who was lost for the season with a torn anterior cruciate ligament in his right knee suffered Friday night.
It was the first time this year Rodriguez pitched two innings and he didn't bounce back well. On Monday he said he was sore and played pregame catch under the watch of vice president of medical services Stan Conte. At the time, Rodriguez said he didn't think it was serious.
But Rodriguez said Tuesday that he felt the muscle knot up after that catch and went for an MRI exam, which revealed the strain.
"It's terribly disappointing," Rodriguez said. "It's just one of those things where I want to come back up and help out in whatever way possible. And when something like that happens you just don't know what to tell yourself at that point. And you're mentally frustrated and you're upset with yourself, because for me I felt like I didn't do enough to keep myself healthy. It's another learning curve in my whole career."
The injury is the same one that sidelined Clayton Kershaw for a month earlier this year.
"They said it wasn't as bad as Kersh's," Rodriguez said. "It was the same kind of diagnosis. Hopefully, it's 15 to 20 days."
Rodriguez hopes to begin a throwing program in three to five days, after the swelling has gone down.
Any injury is serious to the Dodgers and their bullpen. They've already lost Chris Withrow for the season to Tommy John surgery. Chris Perez went on the disabled list Monday with bone spurs in his ankle, which have bothered him for several months. Stephen Fife is on the Albuquerque disabled list with arm issues. Onelki Garcia hasn't pitched this year after elbow and knee operations. Scott Elbert is still in Albuquerque trying to return from three elbow operations.
Javy Guerra was claimed off waivers by the White Sox and is in their big league bullpen. Rule 5 Draft pick Seth Rosin also was claimed off waivers and now is in the Phillies' Minor League system.
Manager Don Mattingly said the injuries will give younger pitchers a chance to make an impression. Carlos Frias, who was called up Monday after Perez went on the disabled list, pitched two scoreless innings in his Major League debut. And Baez will begin his third stint with the Dodgers this season.
"You see Carlos last night, it opens the door for him to get opportunities to go," Mattingly said. "He looked pretty good. Pedro, as he's come in and filled in, he's thrown the ball well, and he's a guy with a quality arm.
"We're testing our depth a little bit, with the young guys, but it's an opportunity for them to step up and show something."