Brian O'Driscoll believes it is "crazy" that Rory Best is not already heralded as one of Ireland's great captains.

Ulster stalwart Best has skippered Ireland since 2016, steering Joe Schmidt's side to the 2018 Six Nations Grand Slam, the maiden two victories over New Zealand – and now to the top of the world rankings for the first time.

Evergreen hooker Best came in for fierce criticism in the wake of Ireland's record 57-15 loss to England at Twickenham on Saturday, August 24.

Ireland hit back with home and away wins over Wales to top the world rankings, leaving boss Schmidt and captain Best in revived spirits ahead of Sunday's crucial World Cup Pool A clash with Scotland in Yokohama.

"I've been incredibly impressed with his diplomacy skills," said O'Driscoll.

"Even when he's felt he's been on the receiving end of a bad refereeing decision, it's the look he gives, more than throwing his toys out of the cot, that's what referees want.

"They know he's annoyed, they know he thinks they've got it wrong, but they accept the respect part that he doesn't berate them or have a go at them.

"That's why he's really influential to this team, and that's why Ireland have had such an incredible disciplinary record, because he talks to referees, respects what they are saying and tries to feed in information to them, and steps away when he's told to.

"And I think that level of captaincy has been completely underestimated."