E! News reported Hyland, 23, was at a Quantas-organized event at the Sebel Pier One with her "Modern Family" co-stars Ariel Winter, Sofia Vergara, Julie Bowen, Ty Burrell, and Eric Stonestreet when an overzealous fan allegedly groped her while posing for a photo with her Wednesday.
Hyland pushed him away, but became visibly emotional, teared up and quickly left the event, the report said.
"It is alleged that the man indecently assaulted the 23-year-old woman at about 7:50 p.m.," a police spokesman told E! without naming the suspect.
"Sorry to all the fans outside the #quantas event that I didn't get to say hi to but I had to leave due to an inappropriate touch by a fan," Hyland later tweeted.