After starting brightly, Manchester United headed into the dressing room at half-time 2-0 down at the Nou Camp.
Individual mistakes from Ashley Young and David de Gea allowed Lionel Messi to bag a brace, meaning United had to score three goals in the second half in order to progress.
The Red Devils came out in the second half with the bit between their teeth, but could not fashion an opening.
Conscious that time was running out, Solskjaer called over Rashford to the touchline in order to pass on a message.
That came in the form of a note, which had a new formation written on it, with players’ nicknames denoting where each man should now place themselves.
One camera man behind Barcelona‘s goal caught the moment, and followed Rashford in the ensuing passages of play.
Initially, the England international ran around barking the new orders to his team-mates while clenching the paper in his left hand.
The Spanish TV station which followed the incident claim to have got hold of the note after the game.
The torn piece of paper shows United in a 4-4-2 formation, different from the 4-3-1-2 with which they began the game.
It reads: Vic (Victor Lindelof), Chris (Chris Smalling), Jones (Phil Jones), Ash (Ashley Young); Jesse (Jesse Lingard), Scott (Scott McTominay), Fred, Paul (Paul Pogba); Rash (Marcus Rashford), Anthony (Anthony Martial).
Rashford did not take great care of the note, however, discarding it onto the turf after going down in a challenge from Gerard Pique.
Barcelona goalkeeper Marc Andre ter Stegen then collected the note and read it closely.
The German then followed suit and also dropped it on the floor, turning his attention to a United attack.
The instructions did not work for United, as Philippe Coutinho scored a pearler soon after, which saw the withdrawal of main attacking threats Martial, Rashford and Lingard in the 20 minutes which followed.