Cairns is currently on trial after being charged with perjury and preventing the course of justice in connection to a libel case he won against former Indian Premier League chairman Lalit Modi.
McCullum told Southwark Crown Court that Cairns had reached out to him in India during the inaugural season of the Indian Premier League and explained spot-fixing in great detail.
Cairns told McCullum that a single event of spot-fixing in a match can fetch anywhere between US$70,000 and US$200,000.
According to McCullum, Cairns had mentioned that former New Zealand players Daniel Vettori and Jacob Oram “did not have the balls to do it”.
The second approach happened in June 2008 over a brief telephone call, after which Cairns told McCullum "Remember, this conversation never happened".
The explosive wicket-keeper batsman also admitted that he did not want to “rattle” Cairns as he still considered him a friend.
"I didn't want it to be true, he (Cairns) was someone I still considered a friend,” McCullum told the jury.
"I didn't want to rattle him, for want of a better term."
McCullum eventually reported the approach made by Cairns to the International Cricket Council (ICC) anti-corruption authorities ahead of the 2011 Cricket World Cup.
The 34-year-old also admitted that a talk given by the ICC’s Anti-Corruption and Security Unit to the New Zealand team motivated him to report against Cairns.
Earlier this week, former New Zealand player Lou Vincent claimed that Cairns had ordered him to spot-fix matches in the now defunct Indian Cricket League.
The trial continues.
© Cricket World 2015