Despite Manchester City's victory over United on Monday, which took them back to the top of the table on goal difference with just two matches remaining, Mancini continues to regard his team as underdogs.
His theory is that United have an easier run-in, which in some senses is correct given City must travel to face in-form Newcastle on Sunday.
However, Ferguson does not believe that is any basis for thinking City are going to blow their chance to secure a first championship since 1968.
"What do you think?" said Ferguson when Mancini's theory was put to him during Thursday's press conference. "They've got two games left. If they win their two games they win the league.
"People talk about goal difference, but it depends how many they win by. Say they win 3-0 on Sunday, their lead would be 11 and they still have QPR at home. That would be impossible."