Rooney's third goal of the season came on Wednesday in Braga from the penalty spot.
That was after missing his fourth spot-kick this year against Arsenal the previous weekend.
Ferguson said: "I told you that I am taking the next one if he misses.
"Wayne has to accept he has to have a better strike-rate with his penalties. His penalty the other night, even though he slipped, was well struck and it hit the target. He has to accept that he has to produce better, but he is capable.
"The one thing about Rooney is that it wouldn't matter if it was a World Cup final or a Rumbelows Cup first round against an amateur team, he would still want to score.
"His temperament is that, if he misses, it won't affect him and that is important for a penalty taker.
"That can be an issue with lots of players who take penalties. If they miss it, how they handle it can be a problem, but Wayne is good that way. He has the right temperament."