The Algerian has joined the Hammers on an initial season-long loan, with an agreement in place to make the move permanent in a deal which could eventually be worth £30million.
Benrahma scored 17 goals and racked up 9 assists as part of Brentford’s ‘BMW’ front three last season, alongside winger Bryan Mbeumo and striker Ollie Watkins, who has already made his mark in the top flight this season with Aston Villa.
"What I'm looking for is, he scored 17 goals last season, the season before 14 goals and something like 10 assists," said the Hammers boss.
"So you're asking me what I want him to bring to the club? I want him to bring these goals and these assists to the club.
"That's what I see. Now granted, can he step up from the Championship to the Premier League? Well, that's the bit. But that's the level we asked the likes of Jarrod Bowen, can he do it?
"Over the years of my career could Leighton Baines do it, could Phil Jagielka do it, could Tim Cahill do it, could Joleon Lescott do it?
"Could any of these boys step up from the Championship and become Premier League players so that would be the challenge for Said?
"But if he can bring his goals and his assists to our team, with what we've got at the moment it will be another extra dimension which we'll bring to the team.”
Benrahma was not signed in time to face Tottenham on Sunday but could make his Hammers debut at home to Manchester City on October 24.
Additional reporting by PA.