The Red Devils signed Lukaku in a £75m deal from Premier League rivals Everton in the summer transfer window after seeing off competition from defending champions Chelsea.
The 24-year-old made a promising start to his Manchester United career following a return 10 goals in his opening nine games in all competitions.
Lukaku, though, went on a six-game goal drought before he scored in a 4-1 win over Newcastle United earlier this month.
But any suggestion his strike against the Magpies would trigger another prolific run was quashed following a disappointing three-game run without a goal.
The Belgium international has regularly faced questions about his ability to thrive in the Manchester United team.
Former Chelsea defender Townsend claimed that Lukaku is lacking one key quality that made Shearer and Wright such legendary Premier League strikers.
“I get a feeling when I watch Lukaku that in any one game he will prove to be as ruthless as Wright or Shearer was,” Townsend told BBC Radio 5 Live.
Lukaku scored 25 times in 36 games in the Premier League last season to finish behind Tottenham Hotspur’s Harry Kane in the goal-scoring charts.
The Belgian forward has played for Anderlecht, Chelsea, Everton and West Brom during a prolific career so far.
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