The Ligue 1 leaders host their Spanish counterparts on April 2 at Parc des Princes and Ancelotti has said that although his side are not favourites heading into the tie, Barca are not invincible.
"We will not be favourites, but I do not think an unbeatable team exists in football," Ancelotti told reporters.
"On paper, Barcelona have more of a chance to reach the semi-finals, but anything is possible and this is what makes the beauty of our sport.
"I trust and I know that in this tournament we can qualify."
The second leg of the tie will played one week later at Camp Nou.