1) Kylian Mbappé vs. Dortmund's high but slow defensive line

Dortmund have been playing with a back three of late, with Lukasz Piszczek, Mats Hummels and former PSG academy graduate Dan-Axel Zagadou lining up from right to left. With the Yellow Wall behind them, the hosts will expect to have plenty of the ball, and in Hummels, they have a fine player at the heart of it all, able to distribute from deep.

But the problem for Dortmund is when they don't have possession. Hummels has never been the fastest player, and Zagadou's physicality was always more about power than pace - part of why he was never able to displace Thiago Silva from the first-team set-up in the French capital before leaving in 2017. If PSG win the ball back with Dortmund trying to play the game in their half, they have a not-so secret weapon ready to take advantage.

Reducing Mbappé's game to raw pace may not be doing him justice, but he did clock a top speed of 38 kilometres - nearly 24 miles - per hour when PSG beat AS Monaco 3-1 in April last year, and Dortmund don't have a centre-back on their books who could keep up with him at close quarters, let alone when they give the 21-year-old nearly half of the Signal Iduna Park in which to stretch his legs.

Mbappé has scored a team-high 15 league goals for PSG this season, meanwhile, and a further five on the continent, and as if his eye for goal wasn't enough, Dortmund goalkeeper Roman Bürki only saves 50 per cent of the shots he faces…

2) Marco Verratti's midfield merry-go-round

The above assumes that Dortmund will indeed enjoy the lion's share of possession, something Verratti and his midfield colleagues will have something to say about. PSG have boasted a Ligue 1 Conforama-high 62 per cent of the ball this season, and within that, the Italian midfield maestro has misplaced a pass less than seven percent of the time.

Dortmund are missing creative midfielders with Julian Brandt and their captain Marco Reus injured. Emre Can has been drafted in from Juventus, and will take his place in the hosts' midfield alongside Axel Witsel in a double pivot.

An alien flying past the Signal Iduna Park may not fancy the chances of the 1m65-tall Verratti and his 1m74-tall partner in crime Idrissa Gueye winning their midfield battle of attrition against Dortmund's relative giants - who both stand comfortably clear of 1m80 - but no matter how athletic Dortmund's midfield looks, nobody can run faster than the ball can move. And nobody can move it faster than PSG's midfield.

3) A returning Neymar in behind a departing Hakimi

Neymar Jr. has missed PSG's last four games though injury, but is expected to be back for the Dortmund game. With the Brazilian superstar to call upon, Thomas Tuchel is able pick his full complement of world class attackers against his former employers: the Fantastic Four of Mbappé, Neymar, Mauro Icardi and Angel Di Maria.

Where Dortmund are likely to line up in a variation of a 3-4-3, PSG have looked most deadly utilising a 4-4-2 when they have had each of the aforementioned available. A central attacking player when he first joined Paris from Barcelona as the world's most expensive player in 2017, Neymar has flourished playing on the left of midfield in Tuchel's new system.

Up against him on the right flank will be Real Madrid-owned Achraf Hakimi, a player Dortmund have leant on more heavily than any other in Europe this season. A wing-back, the Madrid-born Moroccan has scored a BVB-best four goals in the Champions League this term, including a double against Inter Milan in the group stages.

But he didn't get those goals by paying close attention to his defensive duties, and with PSG boasting the best player in the world not called Lionel Messi or Cristiano Ronaldo, Neymar's presence on Tuesday could prove more costly for Dortmund than it ever did for PSG.