TAMPA -- Yankees outfielder Clint Frazier suffered a setback in his concussion recovery.

The 23-year-old was sent for an MRI before Friday's 5-4 win over the Braves at George M. Steinbrenner Field. On Thursday, Frazier's working "didn't go as well as we hoped," manager Aaron Boone said.

The Yankees are gradually increasing Frazier's workload as the works to come back from persistent headaches that he's described as intense pressure on his forehead.

"Clint came in feeling OK (Friday) morning," Boone said. "But, again, (Thursday) when we upped his workload, it didn't go as well as we had hoped. So with the concussion thing, we're going to be very careful, very cautious with it. Try and listen to him the best we can.

"He went in (Friday), I think right before the game he got an MRI just to kind of make sure we're hitting on everything and getting as many answers as we can. We'll see what the results are from that and just continue to gradually try and build his workload and see how he responds each day to different things."

It's Frazier's first concussion.

He suffered it after hitting his head twice making catches against the left-field wall in Saturday's win over the Pirates at LECOM Park. Frazier said there's a scoreboard directly behind the chain link fence that serves as a wall and the he believes his head whacked it.

Frazier said Thursday morning that he was feeling better. He had been scheduled to see a doctor Sunday.

Frazier has an outside shot at making the Yankees' Opening Day roster.

Fifth outfielder Jacoby Ellsbury suffered a right oblique strain before Friday's game and was scratched from the lineup. It's unclear how much time the 34-year-old will miss.

Brendan Kuty may be reached at bkuty@njadvancemedia.com. Follow him on Twitter @BrendanKutyNJ. Find NJ.com Yankees on Facebook.