Mbappe for once fails to deliver to leave PSG up against it
Ousmane Dembele and Vitinha scored PSG's goals in a 3-2 defeat at the Parc des Princes which leaves them with work to do to rescue the tie in next week's second leg.
They will surely need Mbappe to be at his best in that game on Tuesday at Montjuic if they are to reach the semi-finals for what would be just the third time in 13 years since the transformative Qatari takeover of the club.
"I don't speak about individual players after a game, especially after a defeat," insisted Paris coach Luis Enrique, refusing to criticise his star forward's performance.
"I speak about the team, about my work. There are a lot of things to improve.
"The coach is of course the number one person responsible and I accept it that way."
Scorer of 39 goals for his club this season, Mbappe was described as "invisible" against Barcelona by newspaper Le Parisien, which pointed out that he managed just three attempts on goal during the game, none of which troubled Barcelona goalkeeper Marc-Andre ter Stegen.
In searching for reasons why PSG lost and why Mbappe struggled, the finger could be pointed at the tactics chosen by Luis Enrique.
His decision to select Marco Asensio in the starting line-up did not pay off, and the Ligue 1 side were much improved after the Spaniard was replaced by Bradley Barcola at half-time.
That move saw Dembele switch from the right wing to a position much closer to Mbappe, and both Dembele and Barcola hit the woodwork in the second half.
Not interested?
Luis Enrique's handling of Mbappe in recent weeks is also up for debate, given that the 25-year-old has only completed 90 minutes in one of PSG's seven league games since he informed the club of his plans to leave at the end of the campaign when his contract expires.
Was Mbappe not sharp enough as a result?
"I don't think it had anything to do with his lack of playing time. I got the impression he wasn't interested," said Samir Nasri, the former Arsenal, Manchester City and France star who is now a pundit with broadcaster Canal Plus.
"Without him PSG can't do anything. They need Mbappe to be at his best if they are to qualify."
Credit should also go to the Barcelona defence for their handling of a player they are likely to see more of in the future, given that Real Madrid is his expected next destination.
Playing on the left, Mbappe was up against Jules Kounde, his France teammate, at right-back for Barca, with Ronald Araujo ably assisting him.
"I think we did a very good job of stopping Paris Saint-Germain, not only Mbappe," said Barca coach Xavi Hernandez, who saw Raphinha score twice for his side before substitute Andreas Christensen headed in the winner.
"Both Ronald and Jules were very attentive to those runs behind into space that Mbappe does so well."
Wednesday's Champions League game will end up being Mbappe's last for PSG at the Parc des Princes unless they can produce a comeback in the second leg.
Champions League glory has so far proved elusive for him in his seven seasons at his hometown team, with the closest they have come in that time remaining their defeat by Bayern Munich in the 2020 final.
But perhaps Mbappe simply had an off night.
After all, this is the man who scored a brilliant brace on PSG's last trip to Spain, when they beat Real Sociedad in the second leg of their last-16 tie.
Not to mention his stunning hat-trick in the final of the 2022 World Cup, or indeed a lethal hat-trick on PSG's last visit to Barcelona, in a last-16 clash in 2021 which PSG ended up winning 4-1.