Fergie is getting ready to pick a side to face Real Madrid next Tuesday and he knows that he has to get things spot on for his side to progress any further in the competition.
When the two sides met in Madrid last week there were players who were disappointed not to get a chance, big names such as Nemanja Vidic, Ashley Young were all missing.
And the United boss will have been reminded just what Madrid can do when they trounced Barcelona in the cup, so it is of the utmost importance that Ferguson gets it right.
And for those that don't get a place, Fergie looks back at 1999 to point something out to his hopefuls.
"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 told MUTV.
"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 graciously, 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.
"The players sense it could be a big year for them.
"But at this club, in this situation, anything can happen on the run-in. Players can all of a sudden find themselves playing in a final or an important league game because that is the kind of squad I have."