The 27-year-old was one of two notable absentees alongside Alejandro Garnacho from the Manchester United squad that beat rivals City at the Etihad.
His snub from the Red Devils squad surprised fans given his record against the Citizens having scored six goals in 22 games against them.
Boss Ruben Amorim later insisted that the England international and teammate Garnacho were dropped due to tactical reasons as opposed to any fitness issues.
And according to the Daily Mail, Rashford was then shown the door by United after arriving at the club's Carrington training ground less than 24 hours later.
It has been claimed that the two-time FA Cup winner is suffering from a sickness bug.
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But he made sure to adhere to United's policy of turning up to Carrington despite feeling unwell so he could be assessed by the club doctor.
The news outlet states that Rashford was then deemed to have a high temperature by the doctor where he was allowed to return home and recover.
Just a day after being sent home due to sickness, Rashford was back at his old primary school to hand out 420 presents.
And it was there where he dropped a bombshell revelation on his future ahead of the winter transfer window.
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Speaking to journalist Henry Winter, Rashford conceded that he is 'ready for a new challenge' away from Old Trafford after two decades spent at his boyhood club.
He said: "For me, personally, I think I'm ready for a new challenge and the next steps.
"When I leave it's going to be 'no hard feelings'. You're not going to have any negative comments from me about Manchester United. That's me as a person.
"If I know that a situation is already bad I'm not going to make it worse. I've seen how other players have left in the past and I don't want to be that person.
"When I leave I'll make a statement and it will be from me. 100 per cent."
Rashford added: "I'm halfway through my career. I don't expect my peak to be now.
"I've had nine years so far in the Premier League and that's taught me a lot, that's helped me grow as a player and as a person.
"So I don't have any regrets from the last nine years.
"I won't have any regrets going forward because I take things day by day and sometimes bad things happen, sometimes good things happen. I just try and keep a fine balance."
Pressed on whether the best is yet to come from him, Rashford replied: "100 per cent. That's my mentality."
talkSPORT understands that United are open to offers regarding Rashford, with club chiefs feeling as though a parting of the ways is the best solution for all parties.
But with his contract at the Theatre of Dreams to expire in 2028, United may be forced into a cut-price sale should they wish to get him off their wage bill.