Paris Saint-Germain are nearing le money time, to use the Anglicism that has gained currency among French commentators without ever being circulated widely in English. It refers to the decisive stage in contests, the moments where top performers step up and prove they are worth the big bucks. Wednesday’s Champions League tie between PSG and Real Madrid fits that bill even if it is only a last-16 eliminator.

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These are the showdowns towards which PSG have been building. It was a yearning for success in such moments that led the Qatar-funded club to obliterate world transfer records last summer when they bought Neymar for nearly £200m before agreeing to splurge £165m on the teenage striker Kylian Mbappé. Those moves shook up European football’s financial order and were intended to give PSG supremacy on the pitch.

“Sooner or later PSG will win the Champions League, I’m convinced of that,” said the former Barcelona midfielder Xavi this week. But until PSG show they can beat the traditional superpowers on grass, doubts will persist no matter how much financial muscle they flex. Nearly seven years on from the Qatari takeover, the club have yet to reach even the last four of the Champions League.

Returning to Spain for the first leg against Real will inevitably trigger painful memories of last season’s attempt to reach the quarter-finals. A wonderful 4-0 first-leg destruction of Barcelona suggested the Parisians had finally cracked how to beat the elite but, infamously, they collapsed to a 6-1 defeat in the second leg.

That humiliation and the yearning for redemption drove their summer spree. Have the top-grade recruits and the lessons learned made them strong enough to go farther? It will soon be revealed.

The last match of this season’s group stage may have contained a clue. After dancing through their first five games, PSG travelled to Bayern Munich confident of confirming a first-place finish. But they started awfully and found themselves overrun, 2-0 down by half-time against a team whom they had thrashed 3-0 in Paris earlier in the group.

Reeling, PSG looked likely to surrender top spot to Bayern in much the same way as they (and bad refereeing) had allowed the tie to get away from them in Barcelona. This time they rallied. Mbappé scored five minutes after the break and PSG topped the group despite losing 3-1 on the night. It was a defeat but not too much of a loss – an improvement, then.

Not that being pitted against Real – rather than Besiktas, whom Bayern face – seems a generous reward for the group winners even if Zinedine Zidane’s side are floundering in their domestic league. There are no such worries at home for PSG, who have a comfortable lead in Ligue 1. But their manager, Unai Emery, has a few tricky selection posers to resolve by Wednesday. The first two are relatively humdrum but the third is a doozy.

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At left-back the choice is between Layvin Kurzawa, who can be exceptional going forward but is prone to shocking defensive lapses, or the more dependable Yuri Berchiche. For the midfield anchor Emery has two options: his preference would be for Thiago Motta but the excellent 35-year-old is not deemed fully fit after missing six weeks through injury. So the manager will choose between the impressive youngster Giovani Lo Celso or Lassana Diarra, the 32-year-old former Chelsea, Portsmouth and Real player whose odd career took another twist when PSG signed him as a free agent last month.

Up front there is further intrigue: might Emery decide not to deploy the attacking trio that PSG moved mountains of cash to assemble? Mbappé, Neymar – who scored his 27th goal of the season in Saturday’s 1-0 win at Toulouse – and Edinson Cavani, the MCN on which the club’s marketing campaigns, as well as their sporting ambitions, are based, started this season like a dream, razing defences like an irresistible hydra.

But there have been stutters recently, especially from Mbappé, whose form was sub-prime even before he was forced to miss matches because of a concussion suffered three weeks ago. On his return Mbappé looked out of sorts and was sent off for an ugly foul against Rennes. Meanwhile Ángel Di María has been scorching in recent months and craves a start against Real, for whom he produced an outstanding performance in the 2014 Champions League final.

A case can be made for starting Di María instead of Mbappé at the Bernabéu but Emery seems unlikely to make it. Di María has blown big chances in the past and Mbappé and Neymar were brought in precisely to deliver at times like this.