Mr Manchee told the court he was unaware that the company in which he was selling shares was at the time the subject of a takeover bid from another company, who were being advised by another Citigroup division.
The "Chinese wall" is alleged to have been broken when Mr Manchee met Paul Davrell while they took a cigarette break and was told to stop trading shares in Toll Holdings, while the proposed takeover from Patrick was in the offing.
Addressing the court, Mr Manchee said: "It didn't cross my mind that Citigroup had any involvement. I didn't ever think at the time that Darwell was telling me something he couldn't."
The Australian Securities and Investments Commission has charged Citigroup with a raft of conflict of interest accusations and two charges of insider trading.
Should Citigroup, which denies that the walls between their trading and merger advisory wings were breached, be found guilty it faces a fine of $800,000 and the threat of being forced to pay compensation to Toll.