This Sunday, the lessons are simple for Thomas Tuchel in front of his TV: like Paris, United will not arrive at best for a crucial match in Group H of the Champions League, Wednesday in Manchester.
Because three days before the reception of PSG, the Red Devils delivered an average performance despite their snatch victory on the lawn of Southampton (2-3, 10th day), the day after the Parisian draw against Bordeaux (2- 2).
Led 2-0 at the break, the players of Ole Gunnar Solskjær displayed their defensive limits in the first period, first on the opening of the score on a corner from Jan Bednarek (1-0, 23rd), before David De Gea does not bow on a sublime free kick from James Ward-Prowse (2-0, 34th).
But the entry of Edinson Cavani after the break changed everything.
In 45 minutes, the former Parisian offered his 7th goal of the season to Bruno Fernandes (60th).
Before allowing United, now 7th, to equalize with a furious head (2-2, 74th) then to snatch a happy success with a new helmet blast (2-3, 90th + 3), his second and third goal in PL.
De Gea comes out injured at the break
And like Paris, Manchester will arrive diminished.
Anthony Martial was not on the scoresheet for this meeting - "fell ill during the night" according to Ole Gunnar Solskjær - nor Paul Pogba, still embarrassed by his ankle from France-Sweden, and who did not replayed since.
We should find the two international tricolors this Wednesday.
A lesser evil for the Mancunians, already handicapped by a long list of injured (Luke Shaw, Eric Bailly, Phil Jones, Scott McTominay) to which was added David De Gea.
The Spanish goalkeeper hurt his left knee when he landed on his post, on the goal of Ward-Prowse.
Replaced by Dean Henderson at half-time, he could miss the European shock of his team.
While Manchester played for 90 minutes in a 4-4-2 diamond shape close to the one who should host PSG, Cavani was the big - and only - satisfaction of the day.
Could it be the surprise of the next starting XI given its explosive entry?