NEW YORK -- Yankees right-hander Masahiro Tanaka is expected to miss at least a month after an MRI taken Tuesday revealed a Grade 1 strain of his right forearm and tendinitis in his right wrist, according to general manager Brian Cashman.
Tanaka had been scheduled to start Wednesday against the Rays, but instead went on the 15-day disabled list a day after he arrived at Yankee Stadium on Tuesday reporting discomfort in his wrist. The Yankees said that the MRI showed no changes to Tanaka's partially torn elbow ligament.
"We want to make sure that this doesn't lead to the more horrific problems that we're trying to avoid," Cashman said after the Yankees' 4-2 win over the Rays.
Tanaka will refrain from throwing for seven to 10 days and then will have to rebuild his stamina with a Minor League rehab assignment. Tanaka is 2-1 with a 3.22 ERA in four starts this season and said he aims to return as soon as possible.
"Nothing really big came out from the MRI or anything, so I feel that I can come back strong," Tanaka said through an interpreter.
Last July, Tanaka sustained a partial tear of his ulnar collateral ligament and was able to avoid Tommy John surgery on the advice of four specialists, opting for rehab.
He returned to make two starts in September and then went through the offseason and spring as a healthy player in the Yankees' estimation; manager Joe Girardi said that he was "shocked" when Tanaka reported his issue Tuesday afternoon.
"I don't think it was in the back of our minds," Yankees left-hander CC Sabathia said. "He looked good, he was healthy and he was starting to throw the ball well. It's discouraging for us and it's tough, but we'll move on and keep going."
Asked if this could represent a precursor to Tommy John surgery, Cashman shrugged and replied, "Could be. I couldn't tell you. No one can answer the question," adding that the Yankees would be treating any of their pitchers with the same caution.
Told of Cashman's comment regarding surgery, Tanaka replied, "It has nothing to do with my elbow, so that's something that's out of the question for me."
Cashman said that the Yankees have "absolutely no regret" about their handling of Tanaka following last summer's ligament tear because they followed medical directives in sending Tanaka for rehab.
"I can't remember any time we've ever gone against doctors' orders. Why would we?" Cashman said. "They're the experts. We follow what they prescribe."
With Tanaka out of commission, the Yankees tabbed right-hander Michael Pineda to start Wednesday's series finale. They plan to keep right-hander Chase Whitley in rotation after he pitched five innings of one-run ball in his season debut Tuesday.
"People have just got to step up. That's the bottom line," Girardi said.
With an open roster spot, the Yankees recalled infielder Gregorio Petit from Triple-A Scranton/Wilkes-Barre prior to Wednesday's game.
Bryan Hoch is a reporter for MLB.com. Follow him on Twitter @bryanhoch, on Facebook and read his MLBlog, Bombers Beat. This story was not subject to the approval of Major League Baseball or its clubs.