Yankees starting pitcher A.J. Burnett looks at his hand while...

Yankees starting pitcher A.J. Burnett looks at his hand while pitching in the top of the second inning against the Tampa Bay Rays at Yankee Stadium, Saturday. (July 17, 2010) Credit: Christopher Pasatieri

After the Yankees said Sunday that Andy Pettitte is headed to the disabled list with a strained left groin, Joe Girardi issued the closest thing, for him, to a public challenge. "Someone," he said, "is going to have to step up."

A.J. Burnett, we're looking at you.

Only a few hours after he apologized to his teammates Sunday for failing to control his anger during Saturday's game, the spotlight on him became even brighter. Solving the enigma that is Burnett suddenly carries more weight for the success of the Yankees this season.

Brian Cashman thinks Pettitte could be out a month, but at this point that's just an educated guess. The MRI showed only a Grade 1 strain, which is the best-case scenario. But Girardi aptly pointed out that "you have to treat the patient" and not the MRI. And considering this patient is a 38-year-old who has logged more than 3,000 innings, expect the Yankees to treat his rehab in the most cautious manner. That puts the onus on Burnett to right himself as soon as possible.

There already was a good amount of intrigue surrounding Burnett's next start Friday because it will be his first time on the mound since he went all Kevin Brown on the clubhouse door and cut his hands. And now, with Pettitte out, there are going to be even more eyes on Burnett, because he's needed.

For the past two months, the Yankees' deep rotation afforded them the luxury of not having to worry much about Burnett's maddening struggles. He's been pulling this Jekyll-and-Hyde act throughout his career, so the Yankees have always been confident that he eventually would right himself.

That much hasn't changed. But when you list the reasons why the Yankees have the best record in baseball more than halfway through the season, you have to start with their rotation.

The Yankees' starters are second in the American League with a 3.73 ERA and first with a 1.24 WHIP, and those numbers are even more impressive given Burnett's 8.15 ERA and 1.81 WHIP in his last eight starts.

A big reason for the Yankees' strong rotation has been the renaissance season that Pettitte has been enjoying. At 11-2 with a 2.88 ERA, Pettitte essentially has been the ace even more than CC Sabathia because he's been consistently reliable and effective from the very first day.

This is not to say the Yankees are in trouble without Pettitte. Sabathia has found a groove. Javier Vazquez has turned around his season. And Phil Hughes is fulfilling his potential.

The point is, without Pettitte in the rotation, Burnett has lost some of the cushion he's been provided this season, which has allowed him to struggle without significantly painful consequences to the team. But with a fill-in such as Sergio Mitre or Dustin Moseley behind him filling out the rotation, there's more pressure on Burnett to fix his issues.

"We have to weather this," Girardi said of losing Pettitte. "That's our job, to weather this."

What an interesting weekend this turned into for Burnett, beginning with his self-inflicted injury. And though we're still very much in the moment here, these two days sure appear to have the potential to be a turning point for him.

On one hand, it's easy to envision Burnett suddenly morphing into the dominant pitcher who was 6-2 with a 3.28 ERA after 11 starts, the one who had allowed two runs in 132/3 innings in his two most recent starts before Saturday. But at the same time, isn't it just as easy to see him responding to the additional responsibility that comes with Pettitte's absence by regressing to the pitcher who went 0-5 with an 11.35 ERA in June?

What's hard to envision is somewhere in between the two extremes. Finding middle ground has been a challenge throughout Burnett's career.