Scholes' spell in charge of Oldham started brightly with a win, but he failed to pick up another victory in his next six games and left with the side languishing in 14th place in the fourth tier.
Messi was among 10 players rested for the goalless draw against Huesca on Saturday.
United were gifted a first-half lead when Robert Snodgrass's clumsy challenge brought down Juan Mata and Pogba sent his first spot-kick down the middle of the goal.
Solskjaer's men had lost four of their previous five games in all competitions and could easily have suffered another damaging defeat to their chances of a top-four Premier League finish.
Luke Shaw's own-goal meant Barca took a 1-0 victory away from Old Trafford and they can afford to rotate ahead of the return, given they sit 11 points clear at the top of La Liga.
Chelsea, Tottenham and Arsenal are all vying with United for the two places left on offer in the top four
French World Cup winner Pogba was encouraged by how United largely kept Barcelona quiet.
Pique won the tournament for a fourth time in 2015 but in each season since, the Spanish league leaders have fallen at the quarter-final stage.
Tottenham and Manchester City go head-to-head, but Barcelona's clash with Manchester United is the tie of the round.
The world's most expensive player has been sidelined since hobbling off during a French Cup win over Strasbourg on January 23, missing PSG's Champions League last-16 defeat by Manchester United.