Just four minutes.
"There is nobody who can compare to him, so the only time I wasn’t worried about him was when he was receiving treatment," the coach confessed afterwards.
For the other 86 minutes of the game, Marcelino was gripped with fear every time the Blaugrana forward picked up possession, even when the Argentine was clearly hampered by a thigh problem in the closing stages.
That is how terrifying Messi is, particularly right now, in this form, with 14 goals in his last 10 appearances in all competitions.
Valencia went 2-0 up inside half an hour at Camp Nou yet Marcelino knew that with Messi still on the field, nothing could be taken for granted.
His trepidation proved justified, with the 31-year-old pulling a goal back from the penalty spot before levelling matters midway through the second half with a characteristically measured left-footed strike from outside of the area.
Afterwards, Marcelino sounded almost as awestruck as he was frustrated.
"He is not like any other player," he acknowledged. "He is decisive in almost every game, he is extraordinarily talented and he makes any opposition team suffer a lot.
"But this is not new."
On numerous magical evenings for more than a decade, the Barcelona No.10 has singlehandedly turned games on their heads. It's the reason why 'Messidependencia' became a part of football's lexicon.
Of course, Barcelona's reliance upon the five-time Ballon d'Or winner is understandable.
While many do not consider him the best player of all time, it is difficult to dispute his status as the best player in the world today.
Even if those who adore Messi for the aesthetic beauty of his game can be dismissed as 'purists', what can't be disputed is how his superiority is supported by cold, hard facts.
Not only has he scored more goals (29 in just 27 games) than any other player from Europe's Big Five leagues in all competitions, he has also created the most (14 assists).
Nobody else even comes close to matching his combination of innovation and prolificacy.
"The numbers are stratospheric, incredible," Barca boss Ernesto Valverde enthused recently. "Messi is an extraordinary player from another galaxy.
"And it is not just that he is a goalscorer, it's everything he creates, what he generates around him."
In that sense, Messi is more important to Barcelona than ever before.
Where once he had Andres Iniesta and Xavi providing him with service, now he does nearly everything himself. Messi has become both Barca's creator and finisher.
Of course, the man himself distances himself from such talk.
"It's crazy [to say] that the best club in the world depends on just one player," Messi said earlier in the season.
"If that's the case, something's being done wrong because Barcelona
"We're talking about top-level players, the best in the world, and it's crazy to say that Barcelona
It's not, though.
Barca have some fine players: Jordi Alba, with whom Messi enjoys an almost telepathic understanding, is the best full-back in the world, goalkeeper Marc-Andre
However, there is no denying that Gerard Pique, Luis Suarez and Sergio Busquets are no longer quite as brilliant as they once were, which is why managing the seemingly evergreen Messi has become of the utmost importance.
Indeed, even a coach as reluctant to rotate as Valverde has been forced to rest his star man with this month's resumption of the Champions League in mind.
It has not gone well, though.
However, that latter result has to be put in context: Real
Madrid will be a completely different proposition at Camp Nou on Wednesday night, having won their last five games in all competitions under new boss Santiago Solari.
However, speaking after the 2-0 loss at the Ramon Sanchez Pizjuan, Valverde declared, "I do what I think is best for us and the group."
One hopes that he once again adheres to that approach: better to risk losing at home to Real in the Copa than risk their entire season by fielding a half-fit Messi.
A serious injury to the captain would end Barca's hopes of retaining La
As Marcelino says, Messi is not like any other player. And Barcelona would be just like any other team without him.