Brendan Rodgers admitted Celtic were taught a footballing lesson by star-studded Paris St Germain's £424m strike force in their Champions League group stage opener.
The Hoops suffered their heaviest home European defeat as the classy French side ran out 5-0 winners at Parkhead.
Goals from £200m Neymar, £166m Kylian Mbappe, £58m Edinson Cavani, who scored twice, and Mikael Lustig's own goal made it a miserable night for the Ulsterman.
"You have to give them credit, they have shown why they will be up there with a great chance of winning this competition," said Rodgers.
"It was a harsh lesson and a tough lesson."
A spectator entered the pitch during the game and appeared to aim a kick at Mbappe shortly after the visitors' third goal.
As the host team, the Scottish champions could face action from Uefa.