Cincinnati, Ohio - Buffalo Bills safety Damar Hamlin is showing "signs of improvement" but remains in a critical condition in hospital after suffering a cardiac arrest during Monday's NFL game against the Cincinnati Bengals.

The Bills released the update in a brief statement on Wednesday, after Hamlin's uncle Dorrian Glenn revealed the player had to be resuscitated twice after colliding with Bengals wide receiver Tee Higgins.

"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 health care team continues to monitor and treat him."

Speaking to CNN outside the Cincinnati Medical Center, where Hamlin is being treated, Glenn had previously said: "His heart had went out so they had to resuscitate him twice. They resuscitated him on the field before they brought him to the hospital and then they resuscitated him a second time when they got him to the hospital."

Hamlin is thought to still be on a ventilator while sedated to help with his breathing.

Indianapolis Colts safety Rodney Thomas II visited his former high school teammate on Wednesday and told reporters: "I know he could hear me. Even if he couldn't hear me, it didn't matter. I said what I had to say."