Pastore needs help to get confidence back
The Argentine playmaker has failed to meet expectations since he signed from Italian side Palermo for 42 million euros last year and was replaced at halftime in Saturday's 4-0 home league victory over Troyes.
Ancelotti has handed the 23-year-old 10 league starts despite Pastore producing ineffective performances.
"He has a confidence problem, especially at the moment," Ancelotti told a news conference.
"Everybody has to help him pull out of this bad moment," added the Italian, despite having dropped Pastore from the squad for Tuesday's League Cup quarter-final at Saint-Etienne.
"The players have kept faith in him. I am sure this bad moment will come to an end. He is a professional, focused on his work."
Italy midfielder Marco Verratti will also miss the game after he suffered bruising on Saturday. Centre-back Alex also did not make the squad.