Mancini said his side would probably need to win all their remaining games to stand any chance of retaining the title.
The 48-year-old said: "It is difficult because we have 30 points to play for and we need to try to win. At the end, we will see what happens. In football everything can happen right up to the last second.
"We probably need to win all 10 matches that are left. If [United] lose three or four or five games... But it is difficult, because they are too strong for this.
"When you have to win always, it is difficult to win every game. But last year we did this. Why can't we do it this year?"
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