Hyland, 23, left a party hosted by Qantas airlines after a fan grabbed her breast, causing her to scream, "Don't touch me there!" and burst into tears, The Daily Mail reports.
Hyland Tweeted an apology to fans who she was unable to greet due to the incident.
"Sorry to all the fans outside the ... event that I didn't get to say hi to but I had to leave due to an inappropriate touch of a fan," she wrote.
An unidentified 29-year-old man has been arrested in relation to the incident, which took place on Hickson Road in the Rocks at 7:50 p.m., a spokesperson for the NSW Police tells WHO magazine. He has been charged with assault with an act of indecency and granted conditional bail to appear at a local court on March 14.
Hyland's boyfriend, actor Matt Prokop, angrily Tweeted Thursday in response to the assault.
"To the a–––––– who assaulted Sarah tonight I hope to God you don't see next week," he wrote.
"All Sarah wanted to do tonight was to say hi to the girls who were waiting outside one d–––––– can ruin it for everyone. Goodnight," he added.
Sorry to all the fans outside the #qantasevent that I didn't get to say hi to but I had to leave due to an inappropriate touch of a fan— Sarah Hyland (@Sarah_Hyland) February 20, 2014
Reporting by MIA McNIECE