Just six months later, the Argentine played a pivotal role as the Blaugrana became the first European club ever to claim a second continental treble.
Scholes hadn't read the situation incorrectly, though.
A dressing-room bust-up with then coach Luis Enrique after a tame 1-0 loss at Real Sociedad at the turn of the year – later confirmed by defender Jeremy Mathieu – had been responsible for arresting Messi's apathy.
Four years on, Barca are bidding for another treble, with Messi proving even more influential than he was in either 2015 or 2009.
Messi admitted even before the season began that, after last term's domestic double, it was time to conquer Europe again.
He has, therefore, been playing like a man possessed, taking on all-comers on three fronts, intent on achieving something truly spectacular with a squad nowhere near as strong as Barca's previous treble-winners.
Indeed, that the Blaugrana beat Real Madrid on Wednesday night without playing particularly well was hardly a shock. They have, after all, been winning games in unconvincing fashion all season.
However, what was surprising about Barca's 3-0 Copa del Rey victory at Santiago Bernabeu was that the visitors triumphed without Messi at his best.
As former Real Madrid boss Vicente Del Bosque pointed out in explaining why he rates the Argentine above Cristiano Ronaldo, "Messi almost always plays well.
"There are players who never do anything wrong and he has an impressive consistency."
Particularly in Clasicos. No player has scored more goals (26) or racked up as many assists (14) in the fixture's 103-year history. Yet Messi was largely anonymous in the Copa del Rey semi-final second leg; "invisible" as AS put it.
The electrifying but profligate Vinicius Junior had six shots alone; Messi didn't register one. So, while Real may have once again let Luis Suarez run riot, they at least did a fine job in nullifying Barcelona's primary goalscoring and creative threat.
Of course, they did that by any means necessary: on one of the few occasions Messi found some space in between Madrid's defensive lines, he was ruthlessly chopped down by Toni Kroos, while there is still a photo of a desperate Luka Modric holding to the Barca No.10's jersey doing the rounds on social media.
It evoked memories of Marco Materazzi's advice to any team that has the misfortune to come across an in-form Messi.
"In my opinion," the former Inter defender told Goal back in 2015, "you should pray, and then commit a foul on him!"
Such an approach doesn't always work, though. Casemiro & Co. kicked lumps out of Messi at the Bernabeu in 2017, even leaving him with a bloody mouth, yet he kept running at them and ended up scoring a last-minute winner.
Essentially, it is difficult to keep a good man down. Which, of course, is just as well for Barca.
The Blaugrana are already the only club in history to win a continental treble twice. Now, thanks to their clinical Copa win in Madrid, they remain on course for a third.
Messi, of course, is the principal reason why.
Subdued as he may have been against Real, Barca would not have even made the semis had it not been for their captain, who orchestrated second-leg fightbacks in both the last 16, against Levante, and the quarter-finals, against Sevilla.
Such heroics were only required because the skipper had been rested for the first legs. And why had he been rested? Because Messi has been almost carrying Barcelona on his own this season, certainly from an offensive perspective.
Defensive midfielder Sergio Busquets and centre-back Gerard Pique – who, along with Messi, are bidding to become the first players ever to win three trebles – are both proving reports of their demise have been greatly exaggerated, while Marc-Andre ter Stegen is continually performing miracles in goal.
Furthermore, left-back Jordi Alba is Barca's most dangerous attacker after Messi, which also says much about how inconsistently Suarez, Ousmane Dembele and, worst of all, Philippe Coutinho have been performing.
Thus, the responsibility to make something happen almost always falls on the captain's shoulders, making the potential for fatigue obvious.
As former Barcelona striker Sonny Anderson told Goal, Ernesto Valverde needs to play Messi as often as possible while at the same time protecting him from burn-out.
"The team has the quality to play some games without Messi," the Brazilian acknowledged.
“But, as a rule, Valverde has to try to get the most out of him because he is the only player in the world capable of deciding a game on his own.”
Indeed, Barca have scored 100 goals this season; Messi has been directly involved in just under half of them, scoring more (33) and creating more (15) than any other player across Europe's 'Big Five' leagues.
What's more, he has played 33 games; only in seven of those outings did he fail to contribute to a goal, and even two of those appearances came as a substitute.
Messidependencia has existed for some time now but its current scale is truly staggering.
As was his performance in last weekend's 4-2 victory at Sevilla, with the 31-year-old scoring a hat-trick as spectacular as it was important.
Twice Barca trailed at the Ramon Sanchez Pizjuan, twice Messi drew them level with goal-of-the-week contenders – one off either foot.
He then edged them ahead with an exquisite dinked finish with five minutes to go before setting up his struggling strike partner Suarez for a morale-boosting goal in injury time.
Without that strike, who knows if Suarez would have finished with such unerring accuracy against Real on Wednesday? He had certainly struggled to play with such dynamism and precision since last October's Clasico rout of Julen Lopetegui's sorry Real side.
Regardless, Suarez's timely double means that Barca are now perfectly primed for a third treble.
They sit seven points clear of Atletico Madrid at the top of the Liga table, will play Valencia in the Copa del Rey final, and face Lyon in the last 16 of the most wide-open Champions League in years, having drawn 0-0 in the first leg in France.
There are still many massive matches to come, though, starting with Saturday's Liga Clasico at the Bernabeu.
It is Barca's toughest remaining away game but victory would almost certainly reduce La Liga to a two-horse race with Atletico, whom they host in April.
Real, though, will feel that if they take their chances this time, they can propel themselves back into contention.
However, while Barca could again play as badly as they did three days ago, it's unlikely Messi will.
Fatigue could well prove an issue; boredom certainly will not.
The treble is on again. It would be his most impressive yet.