Buffalo Bills safety Damar Hamlin remained in a “critical condition” on Tuesday after collapsing during a Monday Night Football game and receiving treatment on the field.
A statement released by Hamlin's family asked that fans keep him in their prayers.
“On behalf of our family, we want to express our sincere gratitude for the love and support shown to Damar during this challenging time,” the family said through representative Jordon Rooney.
“We are deeply moved by the prayers, kind words and donations from fans around the country.”
The Buffalo Bills team later updated that he is still in "critical condition" in the intensive care unit.
NFL Commissioner Roger Goodell said the Bills-Bengals game would not be resumed this week.
"After speaking with both teams and NFLPA leadership, I decided to postpone last night's game and have our focus remain on Damar and his family," Mr Goodell said in a memo.
He said the league would provide mental health support to the teams.
The league has not made a decision on if the game will be resumed at a later date, and it has not made any changes to the Week 18 schedule.
Mr Rooney tweeted on Monday night that Hamlin's vital statistics are “back to normal and they have put him to sleep to put a breathing tube down his throat”.
Partway through the first quarter of the game between the Bills and the Cincinnati Bengals at Paul Brown Stadium, Hamlin took a hard hit during a tackle, stood up and then collapsed to the ground.
The Bills confirmed that Hamlin had suffered cardiac arrest and that his heartbeat was restored on the field in Cincinnati before being transported to the UC Medical Centre.
Players from both NFL teams gathered around Hamlin while he was being treated, with many of them kneeling and others weeping.
The crowd in Cincinnati remained silent and television coverage broke away from the scene on the field.
Bills owner Mike Brown said in a statement on Tuesday that “humanity and love rose to the forefront” as athletes and fans across the US demonstrated their support for Hamlin.
ESPN said the 24-year-old Hamlin was provided with oxygen as he left after being placed on a stretcher and that members of his family, watching the game, joined him in the ambulance.
After the ambulance left the field, reports initially suggested the game was going to restart following a five-minute warm-up.
But after the two team's coaches had conferred with referees, players were told to head to the locker room, while the game was announced to be “temporarily suspended”.
The NFL then issued a statement saying that league commissioner Roger Goodell had asked the game be postponed and gave details on Hamlin's condition.
“Hamlin received immediate medical attention on the field by team and independent medical staff and local paramedics. He was then transported to a local hospital where he is in critical condition,” the league statement said.
“Our thoughts are with Damar and the Buffalo Bills. We will provide more information as it becomes available. The NFL has been in constant communication with the NFL Players Association, which is in agreement with postponing the game.”
Video footage showed that Hamlin had been hit in the upper chest area.
American football is one of the world's most violent team sports and the NFL has been dealing with growing concerns in recent years over the effects of concussions and other injuries that players have received during games.
Fans donate millions to Hamlin's toy drive
Following the incident on Monday, fans from across the US visited Hamlin's GoFundMe page to support the NFL player's toy drive.
More than $4 million had been raised as of Tuesday afternoon from more than 150,000 donations. The page set an original goal of $2,500.
“As I embark on my journey to the NFL, I will never forget where I come from and I am committed to using my platform to positively impact the community that raised me,” Hamlin wrote when he set up the page.