Sarandon was taking part in a talk about women in movies at the Cannes Film Festival, and addressed the accusations against the director.
“I think he sexually assaulted a child and I don’t think that’s right,” she said.
Sarandon, who was taking part in the Women In Motion talk alongside her Thelma And Louise co-star Geena Davis, declined to comment further on the subject.
Her comments came days after Allen’s son Ronan Farrow reiterated sexual abuse allegations against his father, just as the filmmaker was unveiling his new movie Cafe Society at Cannes.
Farrow wrote a guest column which was posted online by The Hollywood Reporter, resurrecting claims Allen had molested his adoptive daughter Dylan Farrow when she was a child.
His column questioned the festival’s and the media’s continued embrace of the 80-year-old director.
He wrote: “Tonight, the Cannes Film Festival kicks off with a new Woody Allen film. There will be press conferences and a red carpet walk by my father and his wife [my sister, Soon-Yi Previn].
"He’ll have his stars at his side — Kristen Stewart, Blake Lively, Steve Carell, Jesse Eisenberg. They can trust that the press won’t ask them the tough questions. It’s not the time, it’s not the place, it’s just not done.
“That kind of silence isn’t just wrong. It’s dangerous. It sends a message to victims that it’s not worth the anguish of coming forward.
"It sends a message about who we are as a society, what we’ll overlook, who we’ll ignore, who matters and who doesn’t.”
Allen has previously denied molesting Dylan, whose adoptive mother is his ex Mia Farrow. The allegations were first levelled at him in 1992 when Dylan was seven and Allen and Farrow were in the midst of a bitter split.
In 2014, Dylan, 30, published an open letter in the New York Times outlining her father’s alleged abuse. Her brother and mother have said they decided not to press charges in the 1990s due to Dylan’s “fragility”.
Allen later struck back with his own open letter, calling the accusations “ludicrous” and repeating his charge his former partner had “coached” his daughter during their split.
Last week, he said he had “said everything I had to say about that whole issue” in that column.