The 29-year-old former Miss India hurt her lip and said she was "ashamed" after an unidentified person threw a stone at her.
"A stone was thrown at me on stage in Faridabad, it hit and hurt my lip, for the first time in my life, I'm truly ashamed of our people... No, I'm not okay but if they were trying to defeat my spirit, it hasn't worked..," she posted on twitter.
A large number of fans had gathered in Faridabad to catch a glimpse of the starcast of the film, who were supposed to attended an adult party where they were to perform and interact with fans.
"Sarah was unwell since morning. She was not there at any other promotional events but chose to attend this evening only to interact with her fans," a source close to the film said.
"Kyaa Super Kool Hain Hum" also stars Riteish Deshmukh, Tusshar Kapoor and Neha Sharma and is produced by Ekta Kapoor. It will hit theatres on July 27.