Cape Town - Barcelona had not conceded a goal this season but Paris St Germain were convinced the Spanish side, who lost 3-2 in the Champions League at the Parc des Princes on Tuesday, were vulnerable at the back.
Barca, who kept clean sheets in their first seven games in all competitions, looked fragile at the back, especially on the flanks, but that was no surprise for PSG coach Laurent Blanc.
"We watched their games on the video with the staff and we agreed that even though they did not concede, they allowed clear chances to their opponents," he told a news conference.
"They take a lot of risks, it's not easy to defend at Barca, I know it I played there," added the former centre back, who played for the Catalan side in the 1996/97 season.
"They take risks, especially the full backs who attack a lot."
Barca defenders Dani Alves and Jordi Alba had a rough night as Marco Verratti and Blaise Matuidi scored at the far post to put PSG 2-1 and 3-1 up.
Blanc praised his team for being clinical.
"We did not dominate possession, which is a rare thing for us," he said. "But we hit them when we had the ball and it was important that we'd be clinical."
PSG lead Group F with four points from two games, one point ahead of Barcelona. Ajax Amsterdam are third on two points after drawing 1-1 at APOEL, who are bottom with one point.
Barca coach Luis Enrique said: "We knew it would not be easy to qualify. We know it's going to be tough at APOEL, tough against Ajax, too".