Former WorldCom chief Bernie Ebbers has denied claims that he knew accountants were doctoring the books at the firm.
Mr Ebbers sought to distance himself from Mr Sullivan
Speaking in court, Mr Ebbers rejected allegations he pressured ex-chief financial officer Scott Sullivan to falsify company financial statements.
Mr Sullivan "made accounting decisions," he told the federal court, saying his finance chief had "a keen command of the numbers".
Mr Ebbers has denied charges of fraud and conspiracy.
During his second day of questioning in the New York trial Mr Ebbers played down his working relationship with Mr Sullivan and denied he frequently met him to discuss company business when questioned by the prosecution.
"In a lot of weeks, we would speak ... three or four times," Mr Ebbers said, adding that conversations about finances were rarely one-on-one and were usually discussed by a "group of people" instead.
Mr Ebbers relationship to Mr Sullivan is key to the case surrounding financial corruption that led to the collapse of the firm in 2002 following the discovery of an $11bn accounting fraud.
The prosecution's star witness is Mr Sullivan, one of six WorldCom executives indicted in the case,
He has pleaded guilty to fraud and appeared as a prosecution witness as part of an agreement with prosecutors.
During his time on the witness stand Mr Sullivan repeatedly told jurors he met frequently with Mr Ebbers, told him about changes made to WorldCom's accounts to hide costs and had warned him such practises were improper.
However during the case on Tuesday Mr Ebbers denied the allegations.
"I wasn't advised by Scott Sullivan of anything ever being wrong," he told the court.
"He's never told me he made an entry that wasn't right. If he had, we wouldn't be here today."
Mr Ebbers could face a jail sentence of up to 85 years if convicted of all the charges he is facing.
Shareholders lost about $180bn in WorldCom's collapse, 20,000 workers lost their jobs and the company went bankrupt. The company emerged from bankruptcy last year and is now known as MCI.