Barcelona coach Hansi Flick conceded his side were not at Paris Saint-Germain 's level as they suffered a 2-1 defeat at the Olympic Stadium in the Champions League.
Ferran Torres gave Barça an early lead but Senny Mayulu levelled before the break and Gonçalo Ramos struck a 90th-minute winner for the European champions.
The defeat was Barça's first in any competition this season, while holders PSG made it two wins from two in the Champions League.
"You can see it today, there's no point saying we're on the same level," Flick said in the post-game news conference.
"But I believe in my team. Today wasn't our best day, but we are working again to reach this level. Today we lost, but we want to come back.
"We could see the level of PSG and I'm 100% sure we can also play like this