It became a reality for 16-year-old goalkeeper David Gaskell when he attended the Charity Shield fixture against City at Maine Road in 1956.
Tired after working with the Old Trafford groundstaff during the day, the teenager was called into action when Ray Wood was forced off due to injury. Duncan Edwards had temporarily taken over the gloves but Gaskell left the stands to leap into the limelight.
"I'd done my jobs as usual cleaning boots and the baths," he said. "I was in two minds about whether to go to the game as it would be such a rush. My landlady had no idea I had played. Kenneth Wolstenholme never referred to me on the radio commentary. He kept saying Ray Wood was showing his international form!"
Wood at least got the winner's medal sportingly handed over by Gaskell after Dennis Viollet's winner settled the match and the youngster kept a clean sheet. Gaskell's place in United's history was forever secured however, as he remains the youngest-ever post-War player for the Reds. He went on to make 118 appearances for the club and was in goal when Sir Matt Busby won his first trophy after Munich, the FA Cup in 1963.
Happy birthday to David, who turned 71 today.