Kanchelskis believes Mourinho's team will have to beat City twice this season to stand any chance of lifting the title.
With the Pep Guardiola model established, his squad packed with technically gifted and tactically aware devotees, City's level is set.
Kanchelskis - who played for both clubs during his playing career - feels Jose Mourinho's side simply can not afford to lose further ground in their bid to be crowned champions for the first time since 2013. City's last three games, against West Ham, Southampton and Huddersfield, were all won 2-1 with a late goal and have all followed a similar pattern.
As yet, nobody since Everton has been able to restrict them enough to achieve anything other than narrow late defeat but there have at least been signs they are not entirely unstoppable. Firstly, that I had no kind of personal problem with him, no matter what the press said.
Less happily, this is at home, and while the Old Trafford crowd will probably accept a radically reactive approach if it is successful, it's not hard to imagine unease being provoked if it is not.
Further afield, a powerful City season also could have repercussions for an Arsenal side already in visible decline but also a Chelsea team perhaps coming to the end of the brief Antonio Conte era and even a Tottenham side that has begun to look more fragile and a little less likely in the past few weeks.
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They could choose to return to the United States, where they played three matches this summer, or remain in Europe. For City, mounting evidence that they are the Premier League's best side and champions in waiting will be confirmed with a victory on the patch of their greatest rivals.
Fellaini, on the other hand, has been a more short-term problem having missed just the last three games owing to a recurrence of a knee injury he picked up while on global duty.
But having said all that, there are ways United can profit from having Pogba miss the match against Manchester City on Sunday.
"And secondly, that I wanted to show what I could bring to the team, to prove myself". If United prevail, new doubts about City's durability will surface.
"I'm looking forward to this derby because it will be interesting because it is a different Man City now and a different Man United".