"Everyone is worried. Everyone who saw the foul is worried. Of course I'm worried," murmured a downtrodden Thomas Tuchel amid cascades of confetti and ticker tape.

The Paris Saint-Germain head coach had just steered his star-studded team to the French Cup victory after Neymar scored the winner against Saint-Etienne in the final. But their perfect night was soured by a horror injury for highly regarded striker Kylian Mbappe.

The World Cup winner received lengthy treatment after his right ankle was caught by a reckless Loic Perrin tackle in the 26th minute that resulted in a red card for the St Etienne captain and a melee between both sets of players. Mbappe then limped off the pitch in tears and headed straight down the tunnel.

The 21-year-old returned to the bench later in the second half on crutches and watched his teammates finish the business. The extent of his injury remains unclear but his involvement in PSG's fixtures for the rest of the season has been thrown into huge doubt.

The Ligue 1 champions are scheduled to take on Lyon in the French League Cup final next Friday before a potentially explosive showdown with Italian side Atalanta in the quarterfinals of the Champions League on August 12.

Facing a season-defining run of games, Tuchel cannot afford to lose Mbappe, who has scored 30 goals in 33 appearances this term. "We have to be patient because we don't have any news. I think he will undergo tests tonight," added Tuchel, keeping his fingers crossed.

The anxiety was shared by PSG captain Thiago Silva, who said: "I hope Kylian is going to recover as quickly as possible because he's a vital player for us."

It was supposed to be a celebratory occasion as it was PSG's first competitive outing four months after French domestic leagues ended prematurely due to COVID-19. It was also the first official game among Europe's major football powers to allow fans to attend since the pandemic struck in March.

Fewer than 3,000 fans were given the green light to enter the 80,000-capacity Stade de France, with French President Emmanuel Macron the most notable attendee. All were ordered to wear face masks and obey stringent health regulations during the whole process.

For European football, the first tentative steps have been taken towards a return to some semblance of normality. 

For PSG, however, it could be a case of one step forward, two steps back.