Asked whether the slugger would play again this season, Miami manager Mike Redmond said, "I don't know. It's not looking good, that's for sure.
"It's devastating for us. Devastating. For his season to end like that, that's not good."
Players in both clubhouses expressed grave concern for one of Major League Baseball's rising stars.
"I've never in my life experienced something like that," Fiers said, his voice cracking. "It was very hard for me to take in everything at the moment and come back and throw another pitch. I just want to send my thoughts and prayers and everything to Giancarlo Stanton. You never think of throwing at somebody like that. Never in my life has that happened. I just feel very, very sad that I hit him. I'm sorry to their teammates, their fans, his family. It is just tough."
The incident happened with Marlins runners at the corners, two outs and Fiers ahead in the count, 0-1. Fiers threw an inside fastball that struck Stanton on the left side of the face while the slugger was in the act of swinging, according to the ruling of first-base umpire D.J. Reyburn.
Medical officials from both teams rushed to Stanton's side as he lay in the dirt for some minutes, and they eventually removed the slugger from the playing field while he lay on his side strapped to a gurney. Members of the Brewers' grounds crew had to tend to the area before play could resume.
"He had his eyes closed and was laying there. I don't know," Brewers catcher Jonathan Lucroy said. "I just backed away when the trainers ran out. I was just kind of praying that he's OK. I've been hit in the head before like that. You never wish that on anybody."
Of the scene, home-plate Jeff Kellogg told a pool reporter, "For everybody, that was pretty disturbing. [Stanton] stayed pretty much still for the majority of the time. The trainers were out there right away and he stayed pretty much still."
Said Marlins third baseman Casey McGehee: "He was awake, which was good. You could tell it got him good, right away. It's tough to see. It's tough to see a guy in that condition."
Fiers, visibly shaken during the delay, remained in the game only to throw another high-and-tight pitch in the 0-2 count to Stanton's replacement, Reed Johnson, who was struck on the hand -- again during the act of swinging. Before Kellogg could appeal to Reyburn for a ruling, Marlins players rushed the field and Brewers players followed.
"It's up around my face, as well," Johnson said. "I think that's why you started getting some chirping a little bit from our dugout. He was up around everybody's hands and face the whole night. I think that's why the frustration really set in at that point.
"When you're trying to pitch a guy in and you have a tendency to miss up a lot, it's just a bad combination. There were just a lot of balls up around guys' faces tonight. One of them gets our big boy."
Redmond and McGehee were ejected. After the umpires huddled to confirm it was a strikeout, a bizarre inning was abruptly over.
Kellogg cited Rule 6.05(f), which says a batter is out when he attempts to swing at a third strike and the ball touches him. He indicated the crew had watched video replays of each swing and believed they made the right calls.
"I went to the first-base umpire, and he definitely did swing at the pitch," Kellogg said, referring to Stanton. "We've both looked at it and, yes, he did swing -- they both did -- at those pitches."
The Marlins strongly disagreed, in the moment and after the game.
"I felt like if anything, [Stanton] was trying to protect himself," Redmond said. "I know 'G,' he stands two feet off the plate, so for that ball to come up and in on him and hit in the mouth was not even close. If anything, he was trying to protect himself. And Reed's the same way."
The Marlins also were irritated by Fiers' reaction after the pitch to Johnson.
"He hit a guy in the mouth, No. 1" Redmond said. "No. 2, after he hit Reed in the hand, he looks in our dugout, throws his hands up in the air like, 'Hey, why you guys mad?' You just knocked out our best player, hit him in the mouth and then you just hit another guy in the hand. What are we supposed to do? What type of reaction are you thinking that we're going to give you?"
Lucroy characterized Fiers as just as upset, saying the pitch to Johnson was supposed to be a fastball low and away. Instead, Fiers missed badly.
"I don't want to get into the whole feud between both teams," Fiers said. "I understand their feelings. They are thinking about the situation. I understand they have to respect their teammate and back him up. I just hope that Stanton is OK."
"It was a tough situation all around, I think," Lucroy said. "Tough for the umpires, tough for everybody. I was there and I didn't know what to do."
Kellogg issued warnings to both benches. When Marlins reliever Anthony DeSclafani struck the Brewers' Carlos Gomez with a pitch in the sixth inning, DeSclafani and Marlins bench coach Rob Leary were ejected by rule.
"We deal with this, and occasionally it happens. Not very often but it does," Kellogg said. "When you see somebody get hit like Stanton did, that's upsetting to everybody on the field, but we still have to umpire."
Brewers manager Ron Roenicke was asked whether he feared there would be bad blood between the teams in the future.
"I don't think it will cause bad blood, because it was an accident," Roenicke said. "They absolutely know that [Fiers] was not trying to hit him. They're not going to be happy about it. We're not happy about it. But it's just something that happens in this game that sometimes you can't control."