"I think since he's taken over as captain he's done a fantastic job so far in getting New Zealand cricket to play the way that he wants New Zealand to be perceived as and that's a great thing for their sport," Warner told News Corp.
"He's going to leave a big hole experience-wise in that team. You look at the greats like Stephen Fleming and Daniel Vettori when they left, what key roles they had in the game - they played massive roles for New Zealand.
"You're going to see that role get taken away from them again and I think not just from a batting but a leadership point of view.
"I think whoever takes over there is definitely going to have big shoes to fill.
"I'm sure whoever does take that responsibility (Kane Williamson) will do a great job.
"But as a person and a character (McCullum) is one guy I do have the utmost respect for."
McCullum admitted yesterday in a lengthy press conference where he reminisced about his 14-year international career that he won't go down as an all-time great.
A modest Test average of 38.48 shrinks to just 26.16 in matches against Australia.
Warner last year took exception to McCullum on one hand trying to sell the virtues of the 'spirit of cricket' and on the other throwing stones at he and Steve Smith for their behaviour in a series that didn't even involve his team.
But the Australian vice-captain said McCullum was a role model for all cricketers to follow.
"He's always a gentleman and always has been. He's a great person to sit down and have a beer with," said Warner.
"Cricket is losing a true gentleman from the sport."