Brian O'Driscoll fears Toulouse will expose Jacques Nienaber system

Jacques Nienaber is less than one year into his time with Leinster and the results so far are positive.

An Investec Champions Cup final is already booked, and the province sit in second place in the United Rugby Championship table. However, the World Cup-winning coach has been quick to emphasise that it will take a while before his squad fully get on board with his system.

Just as his former Springboks assistant Felix Jones has stressed with England, the defensive system that the Boks executed so adroitly takes time to master.

When deployed well, the blitz defence can be devastating and can be the foundation of a victory. But when incorrectly used, it can have a catastrophic effect on the defending team.

When looking at his former side this season, Leinster and Ireland great Brian O'Driscoll still has his reservations over the blitz defence and when it should be adopted.

Discussing the defensive system on Off The Ball this week, O'Driscoll used Leinster's 20-17 win over Northampton Saints on Saturday as an example of how the blitz defence can be exposed.

The former Ireland captain assessed the system from the perspective of an outside centre- the position he defended so adeptly in throughout his career.

He pointed out instances where the Saints could have exploited weaknesses in Leinster's structure, and fears their final opponents Toulouse may be more successful in punishing them.

"I would hate to defend that blitz defence as a No13," O'Driscoll said.

"One thing I can't get my head around. I understand the blitz defence on phase, I don't get it on scrum. I just don't. I think it's a nightmare scenario for a No13 or a winger to be trying to defend it off a scrum.

"Saints had a really nice play early in the first half and they just picked the wrong option where it was a left-hand scrum, they'd brought the blind winger in and flashed it in front of him to No12. So it was [Fraser] Dingwall who carried and [Tommy] Freeman came short and Finn Smith out the back.

"They actually ended up hitting Freeman and he knocked the ball on, but that goes out the back to Finn Smith and [Robbie] Henshaw's come a mile in and the separation between him and James Lowe is huge. So you've got Finn Smith around the corner running freely with Lowe having to come to him and [Ciaran] Frawley having to close the gate with two men outside.

"So there'll be those things that Toulouse will look at and go 'wow, that was a perfect play, if we run the same lines and pick a slightly different option, there's a strong likelihood that we'll get a break there.'

"I would hate to defend that blitz defence as a No13. You would just feel so vulnerable and then subsequently as a winger you would feel so vulnerable."