Barca were routed at the Nou Camp as PSG star Kylian Mbappe ran riot, netting a hat-trick as his team firmly took control of the last 16 tie against their Spanish rivals.
Lionel Messi had given the hosts the lead from the penalty spot on 27 minutes but after that it was all one-way traffic as Mbappe’s treble and a goal from fellow PSG forward Moise Kean left Barca with a mountain to climb in the return leg in Paris on March 10.
Despite the nature of the defeat, after the match Koeman was seen smiling and laughing with PSG midfielder Idrissa Gueye – whom he previously managed at Everton.
Some fans latched onto the images to rip into Koeman.
“That’s not the Barca way,” wrote one person on Twitter, sharing the incriminating clip, while another claimed he was “disgusted” by the jovial scenes.
“Koeman was literally laughing at the end of the match. [Joan] Laporta should sack him as soon as he is president,” wrote another fan.
“Nah how is Koeman laughing and smiling after that result?” pondered another observer, while one person questioned “why is this guy the manager of Barcelona?”
Others defended Koeman over his interaction with his former player, with one pundit writing that the Dutchman was within his rights to laugh given the mess he inherited when stepping into the Nou Camp hotseat last summer.
“Ronald Koeman laughing his hole off after losing 4-1 at home. He knows what he took over and why he’s there. Don’t blame him.”
“Should he have cried?” questioned another fan.
PSG had been without injured star Neymar for Tuesday’s clash and were also missing influential Argentine winger Angel Di Maria.
Nonetheless, Mbappe stepped up spectacularly for Mauricio Pochettino’s man for a clash in which Koeman later accepted his team had been inferior.
“Surely the result reflects how superior they were. They were effective. In the first half it was more even. In the second half we had problems defensively. They proved physically to be very superior to us,” the Dutchman said.
“Particularly in the second half we have to admit that they were superior. They have shown that they have a more complete team than us. We have to accept it, improve things.
“We knew that this could happen because we are playing against a great team, a physical team with experience, for many reasons that is ahead of us.”
Barcelona famously overturned a 4-0 first-leg deficit at the same stage of the competition back in 2017, although on that occasion the return leg was at a packed Nou Camp and featured a Barca team inspired by Neymar.
This time around, PSG will hope to have the Brazilian fit in time to feature for them in the second leg in three weeks’ time.