United travel to the Spanish capital in the first leg of their last-16 Champions League clash with the La Liga champions this evening, when Ronaldo to face his former club for the first time.
"The responsibility will be with Rafael. Rafael's maturity this season has been fantastic. Obviously Robin van Persie has been sensational but, outside that, Rafa and Michael Carrick are having their best seasons ever," Ferguson told MUTV.
"He's Brazilian so he doesn't fear a thing. I trust him and have faith in him tonight."
You can follow Sports Mole's live commentary of the match from 6.45pm this evening.