The girl, still in a critical condition after being raped and suffering serious head injuries, was attacked on Chryssi Akto beach last month.
Police collected DNA samples from five people who worked on the beach but these proved inconclusive.
However, authorities said they have taken in for questioning a Pakistani man who worked at a hotel in Chryssi Akti.
The 21-year-old left the hotel on the day of the attack after telling employers that he had to go to Athens because a relative had fallen ill.
Police said the gardener was picked up during a random check in Athens.