Owen Farrell has hailed the growing impact of the Vunipola brothers and admits he hates facing Billy and Mako in training.
Having helped Saracens reach second in Pool Three, with a win over Connacht and a slender defeat to Toulouse, the trio have linked up with England.
Billy joined Saracens in the summer and Farrell, who has already booted 24 points in this term's European campaign, has been hugely impressed by the duo.
"They're both big lads. They're massive. I don't like tackling them in training.
"But it's not just that, they have good rugby brains as well. They know exactly what they're doing.
"Mako is the best rugby-playing prop I've ever seen and Billy is a big, big unit who has really good skills and feet. I don't see how you really stop it.
"I don't see how they can't go forward given the way they play. That's not just because of the size of them, but the knowledge and feel for the game that they have.
"What they do is go forward and everyone thinks that is just because they're so big and strong but it's also because of their knowledge and feel for the game."
Mako has grown in influence at Saracens and was an integral part of their march to the Heineken Cup semi-finals last season, playing in all eight encounters.
Billy was equally influential as Wasps reached the last four in the second-tier Amlin Challenge Cup and the brothers have been devastating in tandem at Allianz Park.
Billy's colossal ball-carrying in the European clashes against Connacht and Toulouse has seen him widely backed to pull on the England number eight jersey in the autumn.
And Mark McCall will be hoping the behemoth brothers will continue their impressive form when they return to Saracens at the end of November.
The London club are four points adrift of four-time champions Toulouse and will be aiming to secure a maximum points haul from their back-to-back clashes with Zebre. They kick-off the double-header at Stadio XXV Aprile on December 7.
We continue our build-up to next month's high-profile games with a look back at the day when Ulster took Thomond Park by storm on the way to inflicting the only home quarter-final defeat on Munster in the history of the tournament.