With another meeting against Real Madrid looming next Tuesday, Ferguson knows he must get his team selection right at Old Trafford if United are to stand any chance of progressing to the quarter-finals.
That is bound to mean disappointment for some, as it did in the Bernabeu a fortnight ago. On that occasion, skipper Nemanja Vidic headed a list of high-profile omissions, with Ashley Young and Nani also left out.
After watching Real hammer Barcelona in the Nou Camp on Tuesday, Ferguson knows how important it is that he makes the correct calls.
Yet, even for those who miss out, the United boss can point to a very real example to prove it does not necessarily mean they can never have an impact.
"In 1999, I left Paul Scholes out of the quarter-final against Inter Milan yet he was the one who scored the goal that got us through," Ferguson said.
"I left him out of the semi-final because I couldn't risk him and Roy Keane together as they were both on yellow cards. He accepted it, came on, got booked and missed the final anyway.
"What did he do? He didn't let it affect him. He went on to become one of the greatest players this club has ever had."
l Paulo Di Canio last night ruled out doing a U-turn and returning as Swindon boss.