The Red Devils managed to pull off a transfer coup last month when Manchester United beat Chelsea to the signing of the Belgium international.
The 24-year-old had been heavily linked with a return to the Premier League champions as Antonio Conte looked to bolster his attacking options.
However, Manchester United swooped in to complete a £75m deal to sign the centre-forward from Premier League rivals Everton.
Lukaku will be tasked with filling the goal void left by former club captain Wayne Rooney and Sweden legend Zlatan Ibrahimovic.
The former Chelsea striker scored 25 times in 36 games in the Premier League but questions have been asked about his big-game mentality.
However, ex-Arsenal defender Groves is confident Lukaku will find scoring goals for Manchester United easy.
“Lukaku is only 24, he gets better with every season he plays and has proven Premier League experience compared to the other two,” Groves told bwin.
“He’s playing with better players and will have more goalscoring opportunities. The knock against him has been that he can’t do it in the big games but to be honest, with no disrespect to Everton, in the big games they had less of the ball and less opportunities for Lukaku.
“Now he’s playing for a big club, he’ll score in more big games because United will win more big games. If United win the league, £75m is nothing.”
Lukaku moved to Everton in a £27m deal in the 2014 summer transfer window after Mourinho failed to guarantee the striker regular first-team football.
The Belgian forward has now reunited with Mourinho at Old Trafford despite the Manchester United boss sanctioning his sale at Stamford Bridge.
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