Paul Pogba scored twice and Chris Smalling bagged the winner as Jose Mourinho's side produced a stunning turnaround from 2-0 down at the interval to win 3-2 and put City's Premier League title party on ice.
Lukaku completed 90 minutes but did not have the best of games, and now the Sun has revealed that he could not celebrate the result after the match because he was being sick.
The Belgian striker has received some criticism for his performances this season, after joining United from Everton for £75m in a record transfer between two English clubs.
But he has still scored 26 goals for United this season, 15 of them in the Premier League. He has also scored in every match he has played in the FA Cup so far, with United through to face Tottenham in the semi finals at Wembley.
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Despite last week's incredible come-from-behind victory, United are still expected to miss out on the title to their city rivals. It would take a collapse of monumental proportions for City to throw away their 13-point lead, although Pep Guardiola has warned that it could happen.
Lukaku swiftly recovered from his illness and is expected to start against former club West Brom on Sunday. The wrong set of results could relegate the Baggies this weekend.
If City beat Tottenham on Saturday evening then defeat for United on Sunday would confirm Pep Guardiola's side as champions.