The Red Devils saw off competition from Premier League champions Chelsea to sign the 24-year-old in a £75m deal from Everton in the summer transfer window.
Lukaku will be tasked with replacing former club captain Wayne Rooney and Swedish legend Zlatan Ibrahimovic in the Manchester United team in the 2017-18 campaign.
The 24-year-old striker scored 25 times in 36 games in the Premier League last season to finish behind Tottenham Hotspur rival Harry Kane in the goal-scoring charts.
However, Lukaku will play in the Champions League for the first time this season despite the Manchester United striker’s previous stint at Stamford Bridge.
While Nevin is backing Lukaku to score lots of goals in the Premier League, the former Chelsea winger questioned whether the new Manchester United signing would prove a hit in the Champions League.
“Lukaku will score a whole bunch of goals for Manchester United but will he score them in the big games in the Champions League?” Nevin told Irish radio station Newstalk.
“That’s still a massive question.”
Lukaku scored Manchester United’s only goal in a 2-1 loss to La Liga giants Real Madrid in the Uefa Super Cup on Tuesday night.
The Red Devils have also signed Benfica defender Victor Lindelof and Chelsea midfielder Nemanja Matic in the summer transfer window so far.
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