Lukaku, 25, sustained a hamstring injury last week and missed the recent victories over Bournemouth and Juventus, but is hoping to be available for United's clash with their bitter rivals this weekend.
The enforced loss of Romelu Lukaku has helped United, with more pace and movement in a front three of Anthony Martial, Alexis Sanchez and Jesse Lingard.
Mourinho may well decide to name a totally unchanged lineup, and he should certainly keep the back four the same given how well they worked together against Juventus. After the goal we had five minutes to wake up again.
"You can't even talk about luck, because you have to find your own luck and in this case we just gifted it to them". 'Hopefully, we can win. "It's true they're the favourites because they're in unbelievable form, but this is Manchester United and you never know what can happen". If you want to speak about their football potential we can speak and football potential starts with investment, and after that of course there is a quality of the work, of the organisation - I think that is untouchable.
United are nine points behind the Premier League leaders after 11 matches as they travel to the Etihad Stadium.
"When you play for United, the biggest club in the UK and one of the biggest in the world, you have to get used to that", said Herrera.
The gesture sparked an altercation with Juventus players but it couldn't overshadow the enormity of the result for United, which has struggled domestically but now has a great chance of reaching the knockout stage in Europe.
"The last results gave us good spirit and energy, but the real United we'll see at the end of the season and then we can say if we've had a good season".