Richard Fuld, the disgraced head of Lehman Brothers, was punched in the face in the office gym amid the bank's collapse.
Mr Fuld, who has been testifying on the financial crisis before the US House Oversight Committee, was attacked on a Sunday shortly after it was announced that the banking giant was bankrupt.
Following rumours that the incident had occurred, Vicki Ward, a US journalist, said "two very senior sources - one incredibly senior source" had confirmed it to her. "He went to the gym after ... Lehman was announced as going under," she told CNBC. "He was on a treadmill with a heart monitor on. Someone was in the corner, pumping iron and he walked over and he knocked him out cold.
"And frankly after having watched [Mr Fuld's testimony to the committee], I'd have done the same too."
"I thought he was shameless ... I thought it was appalling. He blamed everyone ... He blamed everybody but himself."