The A's said in a release on Thursday that McCarthy had undergone surgery to alleviate pressure in his head Wednesday night after a CT Scan revealed an epidural hemorrhage, brain contusion and skull fracture.
The release said that McCarthy is alert, awake and resting comfortably, and adds that he has shown signs of improvement.
"Our first concern is Brandon's health, and we are heartened to learn he has shown progress in his recovery after surgery," A's vice president and general manager Billy Beane said in a statement. "We are glad to report he is stable, awake and alert. The team will provide further updates as they become available in the coming days. We would ask members of the media to respect the privacy of Brandon and his family during this time.
"As we travel to Seattle today, Brandon remains in everyone's thoughts as we wish him a speedy recovery."
The line drive deflected off McCarthy's head, and third baseman Josh Donaldson fielded it for the out, at which point all attention turned to McCarthy.
He sat alert on the mound for several minutes after, with head trainer Nick Paparesta by his side, and he eventually stood up and walked off the field under his own power, before being taken to the hospital for a CT scan.
"I just tried to get out there as quick as I could, make sure he stayed down and didn't try to do anything to further injure himself," catcher Derek Norris said. "You try not to let it linger, but it's human nature for it to. Your heart goes out to your teammate. You battle with them throughout the course of the season. But we try our best to let it motivate us to win it for Mac."
Though that didn't happen on this day, it didn't really matter to the A's -- not after watching their teammate experience a pitchers' worst nightmare.
"I didn't know if it hit him in the face or hit his glove," Donaldson said. "I saw it hit off him and kind of go toward my direction, and I was able to field it and get the guy at first. It's scary. It brings things back into perspective a bit. You just never know. Thankfully, everything seems to be OK right now, but an inch here, an inch there, he can be really hurt."
"It was crazy," said Cliff Pennington, who was manning second base at the time. "From the side, I could tell it hit him in the head. I didn't know if it clipped his glove or not, but I knew that it got him good. Obviously, that takes precedence over anything that happened in the baseball game. You just want to make sure he's OK."
Lefty Travis Blackley was called in for long relief duties, and he excelled, pitching three innings of shutout ball -- but only after shaking off the shock that took over the bullpen.
"I tell you, I didn't even think about coming in to pitch at first," Blackley said. "When that happened, you're all just in shock a little bit. We all just stood there with our hands over our mouths. It looked nasty from our angle. And it just kind of clicked after they were hanging around for a second that I was probably going to be the one to go in."
Back in the clubhouse, several players snuck in to check on McCarthy before he left for the hospital. It's not yet known how much time he'll miss, but his absence would leave the young A's without a veteran on their staff, as they face a grueling September schedule that will decide their postseason fate.
"It obviously hurts," Norris said. "He's our No. 1 guy out there."
"We've got some young guys in our rotation, and he's our veteran guy," Blackley said. "He's been there and done that, and I think a lot of guys like to look at what he does out there to get an idea of how to pitch guys. Hopefully, he won't miss too much. Hopefully he'll be able to make his next start."
The 29-year-old McCarthy is next slated to pitch Tuesday in Anaheim against Aybar and Co., though Blackley and Triple-A righty Dan Straily are other options in the likely event he would be unable to go. A concerned Aybar made the effort to get McCarthy's phone number and planned on calling the pitcher.
"You feel really bad. He's a good guy," Aybar said. "You never want to hit anybody over the head, and he's a good guy. Hopefully everything turns out all right and, God willing, that he gets better soon."
"Obviously, you never want to see anything like that happen, no matter what the situation is," Angels pitcher Dan Haren added. "It doesn't matter if it's the last game of the year and we're tied. Nobody likes to see that happen. I know him a little bit, personally, and it was really hard to see. Being a pitcher, I know those things happen. He's a good guy, and I just hope that he's all right."