The Red Devils signed the Belgium international in a £75m deal from Premier League rivals Everton in the summer transfer window ahead of interest from defending champions Chelsea.
Summer signing Lukaku squashed concerns about his ability to adapt to a top Premier League club with an impressive return of 10 goals in nine games in all competitions.
However, the 24-year-old went on a six-game goal drought before Zlatan Ibrahimovic’s return from injury prompted Lukaku to find the net at the seventh time of asking in a 4-1 win over Newcastle United.
Lukaku, though, fired another blank in a 1-0 loss to Swiss side Basel in the Champions League before Ashley Young’s deflected striker secured a 1-0 win at Brighton Hove and Albion.
Ibrahimovic has been a regular from the bench over the last three games and the ex-Sweden international is pushing Lukaku for a starting spot in the Manchester United team.
Former Arsenal defender Keown believes Lukaku needs to improve his mental toughness to compete with larger-than-life Ibrahimovic at Manchester United.
“I have described Lukaku as a pussycat, whereas Manchester United want a lion on display (and we all know which animal Zlatan Ibrahimovic likes to compare himself to),” Keown told the Daily Mail.
“It is about how you get Lukaku to that stage. He was bought to lead the line and score the goals to win the title. That isn’t happening.”
Manchester United finished in sixth place in the Premier League last term but won the League Cup and the Europa League.
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