The Oakland Raiders wide receiver is in stable condition after being taken to the hospital Sunday following a helmet-to-helmet hit from Pittsburgh Steelers safety Ryan Mundy.

The crowd at the Oakland Coliseum fell to a hush as Darrius Heyward-Bey was on the ground and unconscious after Mundy plowed his helmet into the wide receiver – an illegal hit that the game’s replacement officials failed to flag.

Initial speculation was that Heyward-Bey suffered a concussion, but it appears the wide receiver is dealing with a neck injury, according to ESPN NFL insider Adam Schefter.

“Doctors do not believe Heyward-Bey suffered a concussion and it's more of a neck injury that will require further testing Monday,” Schefter tweeted Sunday.

Fans at the Oakland Coliseum taunted the replacement officials for not flagging Mundy for the hit, according to the Associated Press.

The Steelers safety was one of a number of players who preyed for Heyward-Bey as he lay motionless in the end zone.

Heyward-Bey was attempting to catch a touchdown pass from Oakland Raiders quarterback Carson Palmer when he was injured. The team went on to score during the possession in route to a 34-31 win over the Steelers.

Raiders punter Shane Lechler told that he liked the way his team was able to score following Heyward-Bey’s injury.

“I was very impressed with the way, it's a veteran group, how they bounced back and were able to stick the ball in the end zone,” he told the team’s official website. “It was one of those things where you hate to see a teammate go down like that. It's just a bad deal."

Heyward-Bey was taken off the field in a stretcher and gave the crowd a thumbs-up as he was carted off the field.

"You couldn't see him. They had him blocked off, with the cart in the way,” Raiders long snapper Jon Condo told the Contra Costa Times. “You got to take a knee and send a prayer out to him, pray for his safety," Condo said. "When he raised his arm, that relieved a lot, it helped a lot emotionally on our sideline, that he's all right."

Heyward-Bey’s behavior after the hit was encouraging, Raiders head coach Dennis Allen told Yahoo Sports.

"He was able to talk a little bit,” Allen told the website. "He was able to move his extremities, so that was a good sign."

While Mundy wasn’t called for a penalty on the play, a fine is most likely coming his way for the helmet-to-helmet hit, according to Dough Farrar of Yahoo Sports’ Shutdown Corner blog.

“Mundy's fine will be bigger because Heyward-Bey didn't jump right up and walk away, and it certainly would be better for all involved had he done so, but the effect to Heyward-Bey doesn't necessarily mean that Mundy's hit was particularly egregious or dirty,” Farrar wrote.

Mundy told the Contra Costa Times that he didn’t intend to hit Heyward-Bey with his headgear.

"I didn't go in there trying to hit him with my helmet," Mundy said. "Things like that happen so fast. He may have come down to the level of my helmet. I have to see the replay, I don't know."