Guardiola's absence from the touchline and dressing room at half-time due to suspension was highlighted as one of the factors for City's loss.
The 20-year-old forward impressed for the Three Lions over the international break.
Jose Mourinho's third season at Chelsea and Madrid ended acrimoniously and a third campaign at United already looks like heading the same way
"I don't agree with Jose in terms of being disrespectful to them. This was not our intention, just to film what happened last season."
Mourinho's side were blown away on the south-coast as Brighton scored twice in two minute.
"Marcus took a slight knock, but nothing too serious, so we will have a look at that ahead of tomorrow's session(...)"
Lukaku hasn't featured for United since suffering his ankle problem against Arsenal last month.
Sir Alex no longer needs intensive care and will continue rehabilitation
News of his operation was made public by his old club, with a United statement cautiously optimistic about the prospects for the 76-year-old.
Sir Alex Ferguson, the most successful manager in British football, is recovering following the surgery, his family says.
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