For a striker with 11 goals in 10 games this season, and so clearly full of confidence, it seemed odd that his manager felt the need to protect him.
“‘We have something to prove. Lukaku has to score. We have to win,’ is what they say,” said Mourinho. “[But] We have to prove nothing. One match, one result, one performance — that’s not going to change anything.”
But Mourinho knows the focus will be on Lukaku on his return to Merseyside , to see whether the striker often derided as a ‘flat-track bully’ can prove himself on the big occasion on what is arguably his and United’s first real test this season.
Lukaku has made a flying start to his Old Trafford career following a £75million summer switch from Everton, filling the void left by Zlatan Ibrahimovic’s enforced absence through injury with his goals, physical prowess and ebullience up front.
Not even Sir Bobby Charlton, Ruud van Nistelrooy or the club’s all-time record goal-scorer Wayne Rooney made such impressive starts to their time in the famous red shirt.
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Despite that, Lukaku has been unable to escape the perception he is a player capable of bulldozing inferior sides, only to struggle to repeat those exploits when he comes up against bigger opponents.
The stats seem to back up that view — only 15 of the 85 goals Lukaku scored in the Premier League for West Brom, Chelsea and Everton having come against the established top six.
That pattern has continued this season, with the Belgium international scoring against West Ham, Swansea, Stoke, Everton, Southampton and Crystal Palace — all of whom are in the bottom half of the table.
That is why Saturday’s lunchtime encounter at Anfield — a ground where he has scored just once in six games — has assumed such significance for Lukaku.
It is also why Mourinho was so quick to try to ease any sense of pressure building on his star striker, ahead of a game in which so much will be expected of the Belgium international.
Former United skipper Gary Neville acknowledged the importance of the game for Lukaku, and said the striker will ultimately be defined by how he does on such occasions.
“Lukaku has settled in brilliantly and done everything he was asked to do in terms of converting those home draws into wins,” said TV pundit Neville. “But games like this one are the real test.
“When I look back to his recent performances 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’s now got to show the ruthless streak to win the big games for United.
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“He’ll 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.”
Another former United star, Rio Ferdinand, says Lukaku will relish facing a defence that has conceded 12 goals in seven Premier League games this season.
“Going forward, Liverpool are as good as anyone and as entertaining as any team in the Premier League,” said Ferdinand. “But, defensively, they’re still trying to find that balance. They look quite open at times and are making individual mistakes.
“If you’re one of United’s front three, you’d be licking your lips. They could make it difficult for Liverpool’s defenders.
“Lukaku loves to run in behind and has pace, which is something that’s been lacking at United in the last couple of years.
“Now they look a very strong, quick team.”
All eyes will be on Lukaku at Anfield, to see whether United’s £75m investment can step up to the mark on the big occasion — or whether his critics are right and he again fails to deliver.