The French champions defeated Ajax 3-1 on Tuesday to set up a Group F decider with Barca in a fortnight's time.
A more favourable draw will likely greet the group winners in the last 16, but Cavani believes overtaking Marseille at the top of Ligue 1 must now take priority.
"There is plenty of time until the match in Barcelona, so we need to focus on Ligue 1, which is a big goal for us too," he said. "When the match against Barcelona arrives, we will look for an important victory for us.
"The most important thing was the victory and we are just at one step away from going through as group winners.
"We have to be focused on Ligue 1 [for now]."
PSG face Nice, Lille and Nantes before travelling to Camp Nou on December 10.
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