Melbourne magistrate's court was told that in December last year Warne saw a group of passengers misbehaving in the taxi operated by Rajbinder Singh Shahi shortly before the death of 17-year-old Xavier Salmon.
Prosecutors say that after an altercation the passengers disembarked from the cab before Shahi, 28, deliberately drove into the group and killed Salmon.
Defence counsel Paul Duggan told a committal hearing that Warne was likely to be called as a witness if the matter proceeded to a full trial.
Duggan said Warne was driving in suburban Melbourne in the early hours of December 6 when he wound down his car window to say hello to the group in the taxi.
He said the group verbally abused Warne and threw sweets at him, prompting the spin bowler to tell Shahi "get rid of them, get them out of the cab".
Warne is currently in England captaining the Hampshire county team.
Shahi was remanded in custody to reappear on August 28.