The Brazilian centre-back was left out of PSG's squad for Saturday's Ligue 1 game against Rennes because of a knee injury he picked up in the first leg of their quarter-final tie against Barca at Parc des Princes on Tuesday.
"He sustained a blow to his knee on Tuesday," Ancelotti told reporters following PSG's 2-0 win at Rennes. "That's why he was not here.
"I don't know [if he will be available for next week]. We'll see. It's not very serious but we must wait."
The second leg will be played at Camp Nou on Wednesday. The first leg ended in a 2-2 draw.