PSG must be more clinical - Ibramhimovic
The Sweden striker was not happy with PSG's 1-1 draw against Ajax on Wednesday, as the Ligue 1 champions were left to rue a host of missed opportunities.
Laurent Blanc's side had 14 attempts at goal at the Amsterdam Arena, but were only able to get five of them on target in their Group F opener.
Having taken the lead through Edinson Cavani in the 14th minut, PSG were unable to secure all three points as Lasse Schone levelled for the hosts.
After only taking a point against his former club, Ibrahimovic believes PSG can ill afford to be beaten when they meet Barcelona on September 30.
"Let's see what happens in the next game," he said. "We will need to take points there.
"We had good opportunities to score and didn't.
"This is the Champions League – the opportunities you get you need to punish the opponent. We punished them once and they punished us back."
Barca's 1-0 win over APOEL at the Camp Nou on Wednesday will see them travel to the Parc des Princes later this month on top of the group.