The spectre of another disappointing exit from the Champions League hangs over Paris Saint-Germain after a 3-2 first-leg defeat at home left them with a fight to turn around their quarter-final tie against Barcelona in Tuesday's return.

At first, nobody realistically expected this PSG side, in transition with a rejuvenated squad following last year's departures of Lionel Messi and Neymar, to go on and win the Champions League this season.

But the realisation that Kylian Mbappe would not be staying beyond the end of his contract after this campaign helped concentrate minds, with the superstar forward informing the club of his plans after the win over Real Sociedad in the last 16.

Then came the draw for the last eight and semi-finals, which presented the French champions with a favourable path to reach the final.

Luis Enrique's side, who had been unconvincing in scraping through their group but came into the first leg against Barcelona on a 27-game unbeaten run stretching back five months, were saved from any prospect of meeting Manchester City, Real Madrid, Bayern Munich or Arsenal before the final.

Victory against a Barca side who are not the force of old would set up a last-four tie against either Atletico Madrid or Borussia Dortmund, the kindest draw possible even if neither team could ever be taken lightly.

However, PSG's performance against Barcelona last Wednesday made clear Luis Enrique's side are far from the complete team, and their most important player is not in his best form.

Mbappe has scored 39 goals this season and the Parisians need him on his game if they are to go all the way and end the France captain's seven-year stay at the club by winning European football's greatest prize for the first time.

But he did not play well in the first leg against Barcelona, when PSG's goals came from Ousmane Dembele and Vitinha while he toiled on the left flank.

That has raised questions about Luis Enrique's handling of the 2018 World Cup-winning striker.

He has only played a full 90 minutes once in Ligue 1 in seven games since telling the club of his plans to leave, with the coach regularly insisting he needs to prepare for a future without Mbappe.

Donnarumma doubts

Further back, Gianluigi Donnarumma's error-strewn display in the first leg was just the latest example of the Italian goalkeeper's weaknesses being exposed at the very highest level.

Donnarumma was also not helped by the defence in front of him, with Lucas Beraldo -– the 20-year-old Brazilian signed in the January window -– playing just like a young defender who had never previously taken part in such a big Champions League game.

"Little details made the difference and there are things that we can't accept in the second leg," captain Marquinhos said after the game in Paris, in reference to Barcelona's first and third goals in particular.

"We have no choice. We have to go and win there."

Going out in the quarter-finals would be about par for where PSG are just now, but it would be an underwhelming way for the Mbappe era to come to a close, an opportunity missed.

Not that they should be giving up hope –- after all, Luis Enrique was in charge of Barcelona when they beat PSG in the last 16 of the competition in 2017 despite losing 4-0 in the first leg.

Barca went through by winning 6-1 in the return, albeit they had home advantage in that second game.

PSG -– who were not in domestic league action at the weekend -- should also be much stronger on Tuesday as Achraf Hakimi, so influential getting forward from right-back, returns from suspension.

Mbappe may also feel he has something to prove, and if he performs on the night anything is possible.

"I have no doubt that we can turn it around and that we will. That is my objective," Luis Enrique said.