"Yes, but you know Rodri played a lot of minutes with the national team and also the last games with us," Flick told reporters after Barcelona's 4-2 defeat in Paris on Tuesday.
"I spoke with him this morning and I told him that we made this decision, and Marc Bernal started instead. For me, it was a good solution what we did and hopefully he is fresh on Sunday."
Rodri came on after an hour of the game in Paris, as Barcelona's perfect record this season came to an end.
The Catalans had twice come from behind, with Xavi Espart and Lamine Yamal replying to goals by Desire Doue and Lucas Hernandez for the hosts.
Yamal made it 2-2 in the 79th minute, but Vitinha put PSG back in front two minutes later before Fabian Ruiz sealed the victory for the defending European champions.
"I think it was a fantastic game from both teams but we made too many mistakes, especially in possession," Flick said.
"But I also saw a lot of good things. For me it was a great test for us and you also saw today what errors we have to improve to make things better.
"We have to learn from this game. Today, in October, you cannot win titles. You win the Champions League in June."
Flick added that the upcoming Clasico, in which Barca have the chance to go nine points ahead of Madrid in LaLiga, influenced his team selection "a lot".