TAMPA, Fla. -- The Yankees are having Aaron Judge undergo further testing to determine the cause of the lingering discomfort near the slugger's right pectoral muscle, manager Aaron Boone said after Saturday's 8-2 Grapefruit League victory over the Tigers at George M. Steinbrenner Field.

Judge has been proceeding conservatively since aggravating his right shoulder while hitting at the club's Minor League complex earlier this month. Though Judge has continued to perform conditioning and defensive drills, including throwing at distances up to 120 feet, he has not taken outdoor swings since position players reported to camp on Feb. 17.

"I'm a little frustrated for him, just not being able to get our arms around exactly what's going on and why it's been slow moving," Boone said. "The biggest thing right now is trying to get answers."

Boone said that Judge felt discomfort after hitting indoors on Friday at Steinbrenner Field, which prompted the Yankees to send him for several tests, including an MRI. The results of those tests were negative, according to Boone, who said that Judge has been scheduled for another examination on Monday.

"It was more when he went to hit again yesterday; throwing wasn't an issue," Boone said. "It was more getting through a second day of cage BP yesterday. It just wasn't quite right."

Judge was spotted arriving at Steinbrenner Field in street clothes on Saturday morning, when most of his teammates were already out for batting practice and side work. Despite the stalled return to the batter's box, Boone said that he continues to believe Judge could be ready for the March 26 season opener against the Orioles in Baltimore.

"Time-wise, we're still fine," Boone said. "I don't know what we're dealing with here in the next several days. If he starts playing in games a week or 10 days out, he'd be technically fine, but first things first is getting up to that point. And I don't know when that is."

One spring after the Yankees set Major League records by having 30 players serve 39 stints on the injured list, prompting a revamp of their strength and conditioning department, they have continued to deal with injury issues this spring.

In addition to Judge, outfielder Aaron Hicks (Tommy John surgery), left-hander James Paxton (back surgery), right-hander Luis Severino (season-ending Tommy John surgery) and outfielder/designated hitter Giancarlo Stanton (right calf strain) have been limited in the early going.

In the event that Judge and Stanton are both unavailable, the Yanks' Opening Day outfield projects to feature some alignment of Clint Frazier, Brett Gardner, Mike Tauchman and perhaps Miguel Andújar, who played left field for the third time this spring on Saturday.