▶ Watch Video: Buffalo Bills say Damar Hamlin showing “signs of improvement”

As Buffalo Bills safety Damar Hamlin recovers in the hospital after suffering a cardiac arrest, his high school teammate turned fellow NFL player Rodney Thomas II drove to be by his side. Thomas, a safety on the Colts, drove from Indianapolis to Cincinnati – about 100 miles – to visit Hamlin, who collapsed on the field during a game Monday night. 

Thomas and Hamlin played football together at Pittsburgh Central Catholic High School. Speaking to reporters on Wednesday, Thomas said after his friend collapsed, he got a call from his own father, who stayed on the phone with him as the incident unfolded.

Hamlin’s heart stopped twice — once on the field and again at the hospital.

Thomas said when he arrived at the hospital, Hamlin was sedated. “I’m talking to him, I know he can hear me. And even if he can’t hear me, it doesn’t matter – I said what I had to say,” Thomas said.

“Just being able to see him and see his people, it calmed me way down. And it made that trip home easier,” Thomas said, adding that Hamlin is a fighter and he expects him to walk out of the hospital. “There’s no other thought in my mind other than him walking out.”

Both Hamlin and Thomas are 24 years old. After graduating high school, Hamlin went on to play at the University of Pittsburgh, and Thomas, Yale. 

“If you go back home everybody knows Damar, everyone will say the same thing about Damar, his character, his work ethic,” Thomas said. “You’ll hear nothing but positive things following his name.”

On Wednesday, the Buffalo Bills said Hamlin was still in the ICU in critical condition but had shown “signs of improvement.” “He is expected to remain under intensive care as his health care team continues to monitor and treat him,” the team said.

On CBS News on Wednesday, Hamlin’s uncle Dorian Glenn said his nephew has lung damage and can’t breathe on his own. He had been receiving 100% oxygen from a ventilator but that is now down to 50%, Glenn said.

“People who don’t even know us are showing love and support and we’re so thankful for that,” Glenn said. “I know those prayers are helping because he’s definitely recovering … God got a mission for him and that’s why he’s still here.”

It is not yet clear what caused Hamlin’s heart to suddenly stop beating. CBS News medical contributor Dr. David Agus told “CBS Mornings” he believes the player sustained blunt force trauma to his chest “in the exact right spot, at the exact right moment during his heartbeat,” which caused his heart to have an arrhythmia — “not beat effectively to push blood to the brain.”

“What we know with commotio cordis, which is this condition, is that every minute you delay shocking them, resuscitating them, what happens is there’s an increase of 10% in mortality,” Agus said. “They started CPR right away, which is great. My hope is they were able to restore the heart rate soon enough to be able to get blood flow to the brain so there’s no damage there.”