Hyland, who plays oldest sibling Haley Dunphy in the smash-hit US sitcom, was signing autographs with fellow cast members at a cocktail function on Thursday, and reportedly left in tears.
"Sorry to all the fans outside the #qantas event that I didn't get to say hi to but I had to leave due to an inappropriate touch of a fan," the 23-year-old later tweeted.
Police said a 29-year-man had been arrested and charged with assault through an act of indecency. He was bailed to reappear in court on March 14.
The cast are in Australia to film a vacation episode of the Emmy- and Golden Globe-winning series with locations set to include Sydney and the Great Barrier Reef.