United have been in unstoppable goal scoring form this season, netting 32 goals in nine games across the Premier League, Champions League and Carabao Cup with Lukaku helping himself to 11 in 10.
Their first true test of the season looms large on Saturday however when they travel to Anfield to take on their arch-rivals who will be hoping to end Jose Mourinho's undefeated start to the season.
Having shaken off a minor injury problem during the international break, Lukaku is expected to lead the charge for United on Saturday. The former Everton striker is no stranger to high pressure games against the Reds, scoring twice in his first ever Merseyside derby in a 3-3 thriller at Goodison Park in November 2013.
The Belgium international has not scored in his last seven encounters with Liverpool, however, with United great Neville insistent the striker must prove he can be the different in such pivotal games.
"Romelu Lukaku has settled in brilliantly and done everything he was asked to do in terms of converting those home draws into wins, but games like this one are the real test," Neville told Sky Sports.
"When I look back to the Everton striker's recent performance at Anfield he didn't play well, so this is the next step up for him. Going away to Anfield is a big test and his service will be more limited so he has now got to show the ruthless streak to win the big games for United.
"He will be defined by his performances in big matches. You're at a club with aspirations of winning things and a world class striker will be defined by trophies and performances in big matches."
Both United and Liverpool will enter Saturday's match without some of their most influential players on hand. Paul Pogba remains sidelined with a hamstring problem while the increasingly impressive Marouane Fellaini, who scored twice on his last Premier League outing, joining him on the sidelines. Liverpool meanwhile have lost Sadio Mane to injury with Adam Lallana and Nathaniel Clyne still unavailable with respective calf and back problems.