Michael Pineda going on DL

KISSIMMEE, Fla. -- An MRI of Michael Pineda's sore right shoulder showed no structural damage, just tendinitis, a development Yankees manager Joe Girardi termed "great news."

Still, the 23-year-old right-hander, acquired from Seattle in January in the trade for Jesus Montero, will begin his first Yankees season on the disabled list, and the date of his first start remains undetermined.

Pineda underwent treatment, including icing, at Steinbrenner Field in Tampa after an MRI exam on Saturday. The right-hander doesn't know when he'll resume playing catch.

"I'm feeling a little better," Pineda said. "A little sore. I'm a little sad. I'll be OK."

Pineda had experienced soreness in the back of his right shoulder on Friday night.

"I'm pitching this year," Pineda said. "I'm coming back strong."

Girardi, asked if he considered the MRI results good news, called them "great news.''

"We'll be conservative with him,'' Girardi said Saturday. "He'll get treatment and we'll see how long it is.''

The Yankees feared the worst Friday night when Pineda got knocked around by the Philadelphia Phillies. He gave up six runs in 2 2/3 innings, and afterward informed the club that his shoulder was "a little sore."

Once again, Pineda had been unable to generate the kind of velocity on his fastball that he had shown regularly in Seattle, where he averaged 95 mph his rookie season. His fastball Friday was between 89 and 91 mph, with one reading as high as 94 mph, according to the YES Network radar gun.

But a scout who spoke with ESPNNewYork.com's Andrew Marchand said he clocked Pineda between 88 and 92 mph.

The concern about Pineda's velocity caused the Yankees to ask him several times the past few weeks if his arm felt OK, and according to Girardi and general manager Brian Cashman, Pineda always told them it did.

But Cashman said Friday night that Pineda's relatively low gun readings were "a red flag," a sentiment Girardi repeated before Saturday's game against the Houston Astros.

"There was always that curiosity, you know, why isn't it going up higher, and as you're looking for answers we're looking, too, trying to figure out why isn't the velocity where it was last year,'' Girardi said. "Is it the innings, is he just not ready to turn it loose, you know, what is it? None of us are ever really going to know but right now, he's shut down and we'll get him back as soon as we can.''

Pineda also had problems with his mechanics and his control Friday night, and after the game told reporters he was consciously trying to throw his fastball harder. Asked if he thought that might have contributed to Pineda's injury, Girardi said, "I can't tell you exactly what it is.''

Now, the Yankees' starting rotation is as follows: CC Sabathia pitches the opener on Friday against the Rays in St. Petersburg, followed by Hiroki Kuroda on Saturday and Phil Hughes on Sunday. Ivan Nova opens the series against the Orioles on Monday and Freddy Garcia goes Tuesday.

Pineda's injury in his first season after pitching 171 innings in his rookie season recalled what happened last season to Hughes, who followed his 18-win, 176 1/3-inning 2010 season with an injury-riddled and fastball-deprived 2011.

Hughes, too, was diagnosed with shoulder tendinitis and wound up missing three months of the season, finishing 5-5 with a 5.79 ERA.

"They both got tendinitis, but I wouldn't necessarily say they're similar [injuries]," Girardi said. "There's a lot of parts to that shoulder. It's unfortunate that [Pineda] isn't feeling 100 percent but I think we'll get him back here, I really believe that."

Information from The Associated Press was used in this report.