Yankees starting pitcher Phil Hughes sits in the dugout during...

Yankees starting pitcher Phil Hughes sits in the dugout during Monday's loss to the White Sox at Yankee Stadium. Hughes suffered a setback during a bullpen session earlier in the day. (Apr. 25, 2011) Credit: AP

Nineteen games in the books, and this Yankees season features far more positive answers than any reasonable observer could have anticipated -- their 2-0 loss to Phil Humber (!) and the White Sox Monday night at Yankee Stadium notwithstanding.

Two questions loom, however. The first -- what in the heck is going on with Derek Jeter? -- can quite possibly be attributed to the aging process that seemed to take a strong hold last year. Keep an eye on that one. He can't keep hitting leadoff if he doesn't improve.

The second -- what in the heck is going on with Phil Hughes? -- looms as far more daunting and confusing.

Hughes will undergo a right shoulder MRI and circulation testing Tuesday at Columbia-Presbyterian Medical Center, to see if he can find an explanation why he can't rid himself of his "dead arm." The righthander cut short a bullpen session Monday because his right arm still felt numb and weak, and a visit with team doctor Christopher Ahmad led to a decision to finally test the pitcher.

Now Hughes gets upgraded officially to a "concern," as Joe Girardi put it before the game.

"I'm just hoping there isn't anything to be concerned about," Hughes said.

The Yankees regarded Hughes as a 2011 stalwart, someone on whom they could depend for innings and above-average results. Instead, they received three lousy starts and a visit to the disabled list for something that was initially "not an injury" but now vexes the club.

"We talked about when to make the [minor-league rehabilitation] start, so we were pretty much feeling that everything was going to pretty much go according to schedule," Girardi said. "And kind of like our season so far, it hasn't been that, with the rain."

What exactly is going on? General manager Brian Cashman, reached by telephone Monday -- he was in Lakewood, N.J., watching the Yankees' Class A Charleston affiliate -- said that despite this condition that has persisted for weeks, the team hadn't tested Hughes to this point because "he wasn't feeling any pain."

Is this a byproduct of Hughes' jump in 2010 workload? He threw 192 innings last year, including the postseason, after clocking 921/3 innings in 2009. He had pitched 146 minor-league innings in 2006, giving the Yankees the baseline they used to determine Hughes' 2010 ceiling.

"I guess it's possible," Cashman said.

Amid reported rumblings -- most recently by SI.com -- that Hughes' problem can be attributed to his showing up to spring training out of shape, Cashman said, "He showed up heavier than his target weight, but he did our boot camp, and he was fine. That doesn't have anything to do with this."

When new pitching coach Larry Rothschild, who has been in professional baseball for 37 years and has been a big-league manager or coach for 21 years, says, "It's kind of new territory for everybody," then you start to ponder bad possibilities.

A prolonged Hughes absence means more pressure on the erratic A.J. Burnett, who pitched well Monday night in defeat. It means the Yankees need greater returns from Bartolo Colon and Freddy Garcia, both of whom already have contributed, and perhaps veteran minor-leaguers Kevin Millwood and Carlos Silva, too. It means less room for error if rookie Ivan Nova can't straighten out.

It means, if Hughes' situation drags out long enough, a greater urgency to acquire help from the outside come June and July.

So many questions and scenarios, so little clarity. Maybe Tuesday changes that, although not necessarily for the better for Hughes and the Yankees.