Capello claimed earlier this week that United, currently aiming to secure a record-breaking fourth consecutive Premier League title, are not the "war machine" they once were, adding that "they have started to slow down a bit compared to previously".
But Ferguson reacted vociferously, revealing that he is perfectly happy with the position the reigining champions find themselves in - five points behind leaders Chelsea.
"With all the problems we've had with injuries to defenders, I would have definitely accepted being two points off the top of the table by the end of the year," Ferguson said.
"We have come through a key period - if we beat Wigan we will have got through it without too much damage. We've got the experience to do it and the players to do it."
former Chelsea boss Mourinho, who pipped Sir Alex to the Premier League crown in 2004-05 and 2005-06, also expressed concern earlier this week that United are missing the firepower of Cristiano Ronaldo.
But Ferguson again defended his side, insisting that Ronaldo's departure has seen more players getting on the scoresheet.
"I think we've got 14 different goalscorers this season," Ferguson said. "They're all weighing in from different positions.
"So why worry? The important thing is we're winning and we've scored a lot more than at the same stage last season."
United have scored eight more goals than in their opening 19 games last season and have only a point less than this same stage last year.
And if United beat the Latics - who have lost all of their past ten meetings with Sir Alex Ferguson's side - then they will be two points behind Chelsea, with the Blues facing an exodus of players to the African Nations Cup in Angola.