Buffalo Bills safety Damar Hamlin is in a critical condition after suffering a cardiac arrest during Tuesday's (NZ time) NFL game against Cincinnati Bengals.
The 24-year-old briefly got to his feet after making a tackle on the Bengals' Tee Higgins in the first quarter but then fell on his back.
Hamlin's marketing representative, Jordon Rooney, tweeted: "Update on Damar: His vitals are back to normal and they have put him to sleep to put a breathing tube down his throat. They are currently running tests. We will provide updates as we have them."
The game in Cincinnati was halted as medical staff quickly attended to him while players from both teams took a knee. Hamlin was given CPR before leaving the field in an ambulance.
The NFL later announced the game had been postponed.
Hamlin's family came down from the stands to be with him as he was transported to University of Cincinnati Medical Center. Local media said fans from both teams were standing outside the hospital waiting for news, some holding candles.
It was unclear when the game between two AFC contenders with the No.1 seed hanging in the balance would be concluded.
The NFL said in a conference call that the Bills would be returning to Buffalo and a decision on the game would come later.
Fans donated more than NZ$4.8 million to a charity toy drive hosted by Hamlin and Chasing M's Foundation.
Not long after Hamlin was transported by ambulance, fans began to share the Go Fund Me page established by the safety when he played collegiately at Pittsburgh to help provide toys to children during the pandemic.
GoFundMe verified the page and said Hamlin's initial goal of $4,000 was far exceeded by nearly 130,000 donations in the 10 hours after he collapsed on the field.
At 10:30 pm local time, the fund was more than $1.6 million. By sunrise in Cincinnati, donations exceeded $5.2 million.
Hamlin, 24, has been described by teammates as "generous, genuine and caring."
Rooney appeared on "Good Morning America" on Tuesday to share another update.
"The family is in good spirits, we're just taking it minute by minute," Rooney said. "His family is strong, supportive. Obviously, they are worried. Damar is very close with his family."
Rooney asked that fans give the Hamlin family privacy at this time.