On a staff that houses two pitchers 40 and older and another at 38, Phil Hughes wasn’t the favorite to be the first one hit with a physical problem.

Nevertheless, the 26-year-old right-hander was sent to a local spine doctor yesterday after complaining of upper back stiffness which developed Monday when Hughes was covering first base in drills.

“There always are concerns with back issues. We will see how it plays out,’’ general manager Brian Cashman said of the club’s No. 4 starter. “Pitchers have to bend every time they throw.’’

Asked how long Hughes will be sidelined, Cashman pegged his return at “within a week.’’

Manager Joe Girardi agreed with Cashman’s time frame.

“You are always concerned, but it’s upper back in the shoulder blades,’’ Girardi said. “We will see how he is in a couple of days. The good thing is that he was probably ahead of where he would probably normally be at this time.’’

Girardi said he was encouraged the stiffness wasn’t in the bottom of Hughes’ back.

“You are usually more concerned about the lower back, but until it’s gone it’s going to linger,’’ Girardi said.

A long-term problem for Hughes would open the door for Ivan Nova and David Phelps to join the rotation. It also would be a bad way for Hughes to start the final season before he can be a free agent.

A 16-game winner last year, Hughes is on the verge of a big payday next winter if he can duplicate last season’s effort or improve it.

While Hughes was being examined away from George M. Steinbrenner Field, 40-year-old Andy Pettitte and 43-year-old Mariano Rivera threw bullpen sessions.