The Precious actress confessed that she was disappointed by her experience of meeting Cusack because of the comment, though she said that she was sure the star meant well.
"What celebrity was I disappointed by? Oh, and it's not in a mean way, because I know that she meant well," Sidibe recalled during an appearance on Bravo's Watch What Happens Live.
"I met Joan Cusack, who is my favourite favourite - I love her - but, it was before I became [famous] or whatever. I was at some industry party, and she says, 'Are you an actress?' And I said, 'Yeah!' And she says, 'Oh honey, you should really quit the business, it's so image-conscious'."
Earlier this year, Sidibe was promoted to series regular on The Big C.
The 28-year-old's mother previously defended her daughter's weight, saying that obesity runs in her family.
Watch the trailer for Sidibe's Precious below: