Sasaki has apologized to Watanabe in a statement.
"I regret it from the bottom of my heart," he says.
Watanabe is very popular in Japan and has more than nine million followers on Instagram.
In addition to her work as a comedian, she has participated in a number of advertising campaigns and is one of the few "plus-size" models in the country.
In a statement, Watanabe said she was surprised by the statement.
"I am happy with my body shape.
I want a world where you respect each other ", she says.
Last month, Olympic director Yoshiro Mori resigned after being blown away by statements that the women on the board of the Olympics talked too much, behaved inappropriately and were against the Olympic spirit.
The new Olympic director, Seiko Hashimoto, says she will quickly find a replacement for Sasaki.
- The joke was very, very inappropriate, she says.