United were dumped out of the Champions League 2-1 on Tuesday.
Ferguson said on Countdown to Kick-Off: "Let's be honest, it was hard to take, when you think about all the work that was done in terms of preparation for both legs. The players' performance level was fantastic. The support was unbelievable. We didn't deserve that and it's a fact.
"You just couldn't believe it [the red card]. Quite astonishing. I think, in general, we know it was the wrong decision. I think, after looking at the game again a few times, the players were shocked.
"They couldn't recover from it until we lost the second goal and then they galvanised themselves and were fantastic in the last 15 minutes of the match. They were absolutely brilliant and we could've scored five goals. It was a fantastic performance by the players with 10 men but, in that period after the sending off, they played in shock.
"Knowing we'd had a bad decision against us again, we couldn't get going for 10 minutes. Their legs went to water. That cost us. It really did. If it was a justified sending off, in our eyes, it'd have been okay because it was an absolutely brilliant performance tactically. They never made a chance so I think we'd have got through the game."
Is Fergie's assessment right? Or is too much being made about of Nani's red? Give us your shout below...