Sent Down, Hefner May Go on the D.L. PHOENIX - The Mets optioned starter Jeremy Hefner to Class AAA Las Vegas on Sunday, but an elbow problem could land him on the disabled list. He will be examined in New York on Monday. The move cleared a roster spot for Jon Niese, who started against the Arizona Diamondbacks on Sunday in his return from a partial rotator cuff tear. "I'm hurting the team now, so I needed to say something," Hefner said. Hefner has struggled since the All-Star break, posting an 0-2 record and a 9.13 earned run average in five starts. General Manager Sandy Alderson confirmed that the move "more or less coincides with his lesser performance over the last couple weeks." Hefner has battled the elbow problem much of the season, but it became worse recently, he said. "I think it's endurance more than anything," he said, adding: "The first few innings were pretty good, then soured pretty quickly. Once I'd get to the 70-, 80-pitch range, I'm completely out of gas. There's a little bit of pain, soreness, inflammation - however you want to call it. He said he was not certain, but he thought the injury started after he was hit by a line drive from the St. Louis Cardinals" Carlos Beltran during spring training. The team will go back to a five-man rotation, Alderson said, but Hefner could return later in the season for spot starts. He is 4-8 with a 4.34 E.R.A. in 24 appearances this season.