The cast of the ABC series arrived in the city this week to shoot an Australian episode.
The Sydney Morning Herald newspaper reported that the 23-year-old was attending a social function for cast members at a Sydney hotel when she was allegedly groped on the chest by a man who had asked her to pose for a photograph.
Hyland, who plays big-eyed teenager Haley Dunphy, immediately alerted private security guards, who called police to the scene.
Police said in a statement that a 29-year-old man had been charged following the alleged indecent assault.
Hyland later apologised on Twitter to fans for leaving early.