Stanton was driven off the field in an ambulance after being hit in the face by a pitch in the fifth inning.
The Marlins announced Stanton suffered a laceration and was undergoing X-rays and a CT scan. But Marlins manager Mike Redmond acknowledged after the game that he was not optimistic about the extent of the injury.
"We've lost our MVP," Redmond said. "It doesn't look good."
Stanton immediately fell to the ground after being hit by Fiers' 88 mph fastball. Trainers from both teams came to his assistance, and he was placed on a backboard and then a stretcher. The grounds crew even had to use scrapers to remove all the blood from the batter's box before play resumed.
Stanton's father was at the game and came on the field while his son was treated, then left with him in the ambulance.
The team announced Friday that they didn't think Stanton would need surgery.
Marlins outfielder Christian Yelich tweeted out support for Stanton following the game.
That was one of the to hardest things I've ever had to watch here's to hoping Big G is alright and makes a full recovery prayers ur way bud
- Christian Yelich (@ChristianYelich) September 12, 2014The umpires ruled that Stanton swung at the pitch, setting up an 0-2 count.Reed Johnson pinch hit for Stanton and was hit in the hand by Fiers' next pitch. Casey McGehee was in the on-deck circle and starting yelling at Fiers, and both benches and bullpens emptied.
There was some pushing and shoving, but it did not appear any punches were thrown. When order was restored, the umpires ejected McGehee and Redmond.
Fiers appeared to be shaken as he watched Stanton being attended to, and he was still shaken after the game.
"It's very tough," Fiers told reporters. "I've never in my life experienced anything like that. 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 to Giancarlo Stanton. I would never think of throwing at somebody like that. Never in my life has something like that happened. I'm very sad that it hit them. I'm very sorry to their teammates, their fans, his family. It's just tough."
Fiers also tweeted an apology to Stanton after the game.
@Giancarlo818 I am deeply sorry about what happened tonight. I can't imagine what you and your family are going through. (Continue)...
- Mike Fiers (@Fiers64) September 12, 2014@Giancarlo818 my thoughts and prayers are with you at this time. I feel horrible and hope for a speedy recovery.
- Mike Fiers (@Fiers64) September 12, 2014"[Fiers] gets a lot of [strikeouts] on fastballs up, and the ball just got away from him," Brewers catcher Jonathan Lucroy said. "You saw what happened. It was definitely a scary moment. You never wish that on anybody. It's just a freak accident."
Marlins reliever Anthony DeSclafani was also ejected in the sixth inning after hitting Brewers outfielder Carlos Gomez with a pitch.
"He hit a guy in the mouth, No.1," Redmond said. "After he hit Reed in the hand, he looks in our dugout, throws his hands up in the air like 'Hey, why are 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 do you think we're trying to give you?"
Fiers, however, was unhappy with the Marlins' reaction and that there was a benches-clearing incident.
"A lot of tempers were flaring," Fiers told reporters. "For them to think that it was intentional is beyond me, and something I would never do. It was heat-of-the-moment stuff. I just want to make sure that Stanton's OK. I understand their feelings and everything they were thinking. They've got to respect their teammate and back him up."
The beaning of Stanton quickly drew attention around the majors. Toronto Blue Jays shortstop Jose Reyes, who was Stanton's former teammate in Miami, also took to Twitter to send his well wishes to the slugger.
My heart goes out to @Giancarlo818 and his family. I will pray for your speedy recovery. Get well soon bro
- Jose Reyes (@lamelaza_7) September 12, 2014After Washington beat the New York Mets6-2, seven Washington Nationals players gathered in the clubhouse to watch video of the play on a cellphone.
Stanton leads the majors with 105 RBIs and leads the National League with 37 home runs this season. He is expected to head back to Miami on Friday.
The Associated Press contributed to this report.
Stanton Hit In Face In Marlins' Loss
Baseball Tonight Spotlight: Giancarlo Stanton was hit in the face by a pitch from Mike Fiers and had to be carted off as the Marlins fell to the Brewers 4-2.