From Comcast SportsNetARLINGTON, Texas (AP) -- New York Yankees starter Michael Pineda will miss the entire season because of a tear in the labrum of his right shoulder.The Yankees said the right-hander will have arthroscopic surgery Tuesday in New York and be out for about a year."It's a loss," manager Joe Girardi said Wednesday. "He was a guy that we were counting on this year. We traded for him, and unfortunately he's hurt."New York acquired Pineda from Seattle in January, giving up top catching prospect Jesus Montero to get the 23-year-old All-Star pitcher.Pineda felt weakness in his shoulder during an extended spring training game Saturday, which came three weeks after he had problems in a spring training start. The tear was discovered in a medical exam after that.When Pineda experienced discomfort in the back of the shoulder during spring training March 30, the initial diagnosis was tendon inflammation in his right shoulder.Girardi said Pineda wasn't quite himself during spring training, but that the 6-foot-7, 260-pound pitcher was making his starts and doing his bullpens without any complaints of pain."He just felt like his arm was weak, so it explains why it was weak now," Girardi said. "When and where and how and what we did doesn't matter now. What we have to do is more forward and try to get this kid healthy."Pineda was 9-10 with a 3.74 ERA in 171 innings last year as a rookie for the light-hitting Mariners. He's now going to miss an entire season, and possibly more."It's hard because you get a chance and you realize your dream and you have a good first year and you're looking forward to taking the things that you've learned from your first year and applying them to the second year, and you get hurt. It's a frustrating time," Girardi said. "Our job is to make sure that we keep him focused on his rehab and we get him back for next year."The manager expressed optimism that Pineda would return healthy because he's young and strong."He does have youth on his side," Girardi said. "And he doesn't have a ton of mileage in his arm as a younger player. That bodes well for him."The Yankees revealed the extent of Pineda's injury on the same day that 39-year-old left-hander Andy Pettitte made his third minor league start in his comeback from a one-year hiatus.Pettitte allowed three earned runs and seven singles in 5-plus innings for Double-A Trenton. He struck out three and walked one, throwing 59 of his 81 pitches for strikes. Pettitte is still expected to make one or two minor league starts before possibly rejoining the Yankees.Girardi said he felt the Yankees would be OK with the rotation for now because he believes "our guys can pitch. That's the bottom line, guys just have to get it done."As for Pettitte's eventual return, Girardi feels like so many others who assume that "Andy's going to be the Andy when he left."