Never in his career has Ryan Callahan been the subject of trade rumors. Until now, that is, with the March 5 deadline approaching and the Rangers captain apparently on his way to the open market as a free agent on July 1. Negotiations regarding an extension are at a standstill, if not an impasse, with Callahan believed seeking a deal in the neighborhood of seven years at $42 million that is not in the same ballpark as general manager Glen Sather is willing to pay; not even a ballpark as expansive as Yankee Stadium, where the Rangers and Islanders will meet on Wednesday. As such, the Rangers are believed to be in the process of conducting due diligence regarding the rental market for Callahan, though two league GMs told The Post on Wednesday morning the captain’s name had not been broached recently by Sather. “When it’s this late in the season and you’re eligible to become a UFA, rumors are going to be out there,” Callahan told The Post following Wednesday morning’s skate at the club’s practice facility. “Dealing with them is part of being professional, but you have to take them as rumors and nothing more than that.” Callahan, who will turn 29 next month, will be in demand if he gets to the open market. The Rochester native is believed to atop the Sabres’ wish list. His believed asking price is within reason given the history of the market, but The Post has been reporting for more than a month he would be a very difficult re-sign for the Rangers. “I didn’t have any expectations coming into the negotiations of how this was going to go,” Callahan said. “Some go quickly and some take longer than others. “But I’m doing my best to focus on what my job is on the ice and not let this become any kind of distraction. “Sometimes it’s easy and other times I have to work at it, but I don’t think it’s had any impact on my game.” Callahan’s role has diminished since returning from a knee injury on Jan. 3 that sidelined him for the previous nine matches. The captain, who led the team with 40 power-play goals over the previous four seasons while leading team forwards in PP ice time in each of the last three years, lost his spot on the man-advantage unit and essentially has been the club’s third-line right wing as used by coach Alain Vigneault. Indeed, Callahan has gotten a total of 7:27 on the PP in 14 games since returning to active duty. He has scored once in his last eight games, a shorthanded goal against the Caps on Jan. 19, and has two goals in his last 17 and three in his last 26. The captain has nine goals and 11 assists in 37 games, averaging 17:53 per.