The 71-year-old manager has praised the depth and quality of his Red Devils side, and urged every member to be ready to play their part in the league leaders' run-in
The Old Trafford side are 12 points clear at the top of the Premier League table and face Real Madrid in the second leg of the Champions League last 16 – a match a number of players will miss out on.
But just because they will not take to the field against Jose Mourinho's side does not mean they cannot have a huge role to play in the rest of the season, with the 71-year-old reminded of the squad depth that saw Paul Scholes miss a quarter-final against Inter Milan in 1999.
"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," Sir Alex 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.
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"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."
Sir Alex is delighted by the competitiveness of his squad, and has been buoyed by how eager every player is to contribute, but warned the squad members set to play in Saturday's league match against Norwich that they must remain diligent.
"It is very difficult to rotate the squad at the moment," the Red Devils boss continued.
"They all wanted to play against Real Madrid and there were a lot of disappointed players.
"That was fantastic. It is a measure of their own confidence in themselves.
"But we had a chat. I said 'look, don't think for a minute losing a game for Manchester United is a trivial matter'. It is a serious matter."