Serbian Vidic played the entire 90 minutes at Old Trafford against Everton on Sunday but was left out of the side which earned a 1-1 draw at the Santiago Bernabeu against Real Madrid, with Rio Ferdinand coming in to replace him.

Ferguson said it was a risk leaving the 31-year-old out of the Champions League first-leg clash but ultimately believes he did the right thing in rotating his two senior centre-backs.

"I had my doubts about whether I was doing the right thing or not because he was fantastic against Everton but I stuck by what we've been doing with him," Ferguson told The Sun.

"Three days (between games) to my mind was a risk.

"It would have been the same for Ferdinand. If he had played on the Sunday I would have had my doubts whether to play him on Wednesday."

Jonny Evans played both matches for United and Ferguson believes the Northern Irishman is developing into an outstanding player.

The 71-year-old said: "Jonny has emerged as a real top defender and his form has been fantastic.

"The thing about young players – particularly defenders – (is) when you get consistency from them you know you're on the right track with them. I think Jonny has shown great consistency in the last year.

"If you remember what I said about last year, it wasn't until Ferdinand and Evans played regularly together that we got a run going."