Buffalo Bills corner-back Damar Hamlin showed "signs of improvement" but remained in a critical condition after he suffered cardiac arrest on Monday night, the club said.
"Damar remains in the ICU in critical condition with signs of improvement noted yesterday and overnight," the Bills said.
"He is expected to remain under intensive care as his healthcare team continues to monitor and treat him."
Jordan Rooney, Hamlin's friend and marketing representative, said he and the family "all remain optimistic".
“It's just a matter of seeing more positive signs and keep building on that," Mr Rooney told the NFL Network.
He also clarified that Hamlin was resuscitated once on the field — not twice, as was said on Tuesday night. Mr Rooney could say how long it would take Hamlin to recover.
President Joe Biden said he had spoken to Hamlin's family and acknowledged the risk that playing American Football poses.
"It is dangerous. We've got to just acknowledge it," Mr Biden said.
Hamlin collapsed on the field at Paycor Stadium in Ohio, after colliding with Cincinnati Bengals wide receiver Tee Higgins.
Hamlin received medical attention on the field before he was taken to the UC Medical Centre.
Dorrian Glenn, Hamlin's uncle, told CNN on Tuesday night that the player remained sedated and on a ventilator.
“I'm not a crier, but I've never cried so hard in my life," Mr Glenn said. "Just to know, like, my nephew basically died on the field and they brought him back to life.
“We are just taking it day by day. It seems like he's trending upwards in a positive way.”
The NFL announced on Tuesday that the Bills-Bengals game would not be resumed this week and did not provide a timeline for when or if it would be completed.
“The NFL has made no decision regarding the possible resumption of the game at a later date. The league has not made any changes to the week 18 regular season schedule,” the league said.
Photos and videos shared on social media showed sport fans gathering outside the UC Medical Centre in a show of support for Hamlin.
And stars from across the NFL, including Tampa Bay Buccaneers quarterback Tom Brady and former Bengals quarterback Andy Dalton, joined others in donating to Hamlin's community toy drive.
More than $6 million has been raised for the drive since Monday night.
“On behalf of our family, we want to express our sincere gratitude for the love and support shown to Damar during this challenging time,” his family said.
“We are deeply moved by the prayers, kind words and donations from fans around the country.”
White House press secretary Karine Jean-Pierre said on Tuesday that Mr Biden's administration has sent its thoughts and prayers to Hamlin, his family and his teammates.
The PA contributed to this report