Joseph Esmaili, 23, is facing a pre-trial committal hearing, charged with the manslaughter of cardiothoracic surgeon Patrick Pritzwald-Stegmann at Box Hill Hospital on May 30.

Corey Rogers told Melbourne Magistrates Court on Tuesday he saw the surgeon and Esmaili exchange words before the former "chest bumped" the accused.

"I saw the guy bump Joe and Joe reacted," Mr Rogers told the court.

Mr Rogers said the surgeon was trying to intimidate his best friend.

"He's a tall fella, the doctor," he said.

"Joe stepped back one pace.

"It happened that quick."

Mr Rogers said his view of Esmaili was obscured by the surgeon and he didn't see the actual punch nor the surgeon's head hit the ground.

He admitted lying in his police statement when he said he saw the punch.

After the incident, Esmaili was apologetic and crying "but they were tears of anger", Mr Rogers said.

"He was calling himself a f***head and idiot and saying 'sorry'."

Mr Rogers said Esmaili complained the surgeon kept "pushing" him and "he tried to keep his cool for as long as he could".

He said just prior to the incident, Esmaili was drinking a beer stubby and had a six pack of beer with him, but "he wasn't drunk".

The prosecution alleged the surgeon noticed a group, including Esmaili, smoking in the non-smoking area outside the hospital, and called security.

Esmaili then entered the hospital to go to the toilet and had a confrontation with Mr Pritzwald-Stegmann, who told him that smoking was banned, before asking Esmaili to leave.

CCTV footage played to the court on Monday showed the two men talking closely before the accused launches a single punch, felling Mr Pritzwald-Stegmann, who hit his head on the tiled floor.

The hearing continues on Wednesday.

Australian Associated Press