NEW YORK -- The Yankees were relieved to see Masahiro Tanaka “walking around, acting like his normal self” in the clubhouse on Sunday afternoon, according to Brett Gardner, one day after the right-hander was struck in the head by a line drive off Giancarlo Stanton's bat.

Yankees manager Aaron Boone said that Tanaka was diagnosed with a mild concussion following the blow, which registered an exit velocity of 112 mph, and the club is thankful the injury does not appear to have been more serious.

“I feel really good about where he is,” Boone said. “He came in around noon or 12:30 today and was in really good spirits -- he got a good night's sleep, no loss of appetite. I think all the signs are pointing that he really dodged the bullet there. We're encouraged where he is, but we'll take it day by day. Hopefully it's not something that's too long.”

Tanaka was placed into Major League Baseball's concussion protocol on Saturday, and Boone said he could not say if Tanaka would be ready for the first week of regular-season games, because he will need to show that he can resume full activities without generating symptoms.

“Just a very scary incident,” Gardner said. “Unfortunately, when we're doing the things that we're doing, it's tough to avoid. Just immediately, your thoughts go out to him and you're concerned for him. I'm hoping that he's in the clear.”

In response to Tanaka's injury, left-hander James Paxton opted to use a protective “L” screen during his simulated game on the Yankee Stadium mound Sunday, as left-hander Jordan Montgomery did on Saturday.

“After seeing that happen, I just wanted to play it safe, especially first time out there,” Paxton said. “What happened yesterday was so scary, and luckily it doesn't happen very often, but I just wanted to play it safe first time out. Next time, I think it'll be more of a sim game setting, so the screen won't be out there.”

James and the giant hook
As James Paxton stood in the sunshine, he pondered how delightful it was to wear spikes on a clay mound, not the running sneakers he'd been using on an indoor turf hill. Then Paxton reared back and snapped off a few of his trademark curveballs, and he really felt like a big leaguer again.

Facing hitters for the first time since having lower back surgery in February, Paxton appeared dominant, striking out teammates Miguel Andújar, Tyler Wade and Gary Sánchez in succession during his first inning.

“Getting back on the dirt with the guys and facing some of our hitters, it was great,” Paxton said. “I felt good, I felt healthy. It was a good first step for me.”

Paxton has been throwing regularly at an indoor facility near his Eau Claire, Wisc., home, having intended to be ready for big league action in May or June. He has incorporated a new stretching routine that will allow his back to be more flexible than it was toward the end of last season, and he is continuing to tinker with the grip on his fastball to increase spin rate.

“I thought he spun the ball really well for being the first time out,” Boone said. “He looked fairly sharp. I think it was clearly a steppingstone for him, of getting back out there and getting in a little bit of competition against some hitters.”

Because Major League teams are being capped at three exhibition games prior to Opening Day -- general manager Brian Cashman has said those could take place against the Mets, though matchups have not been finalized -- it is likely that the majority of Paxton's tuneup workload will take place against Yankees hitters.

Some big league hitters and pitchers dislike facing players on their own club, but given the talent of the Yanks' lineup, Paxton said he views those showdowns as a positive.

“I think we're pretty lucky we've got some really good hitters. Facing those guys is tough,” Paxton said. “They know our stuff, so I think that'll be more challenging and help us get ready. I'm looking forward to hearing from our hitters and what they're seeing.”

Bombers bits
Left-hander Aroldis Chapman and Sánchez took part in workouts on Sunday, with Chapman throwing in the bullpen. Their Summer Camp debuts were delayed by issues with travel and intake testing, and Boone said both players are “in a good spot entering camp again.”

Up next
The Yankees' Summer Camp continues Monday as the club plans an intrasquad game under the lights at Yankee Stadium. Left-hander J.A. Happ is scheduled to start opposite right-hander Clarke Schmidt, and Boone said the game could last about six innings. The YES Network will air coverage from 6 p.m. to 9 p.m. ET.