A female French backpacker who was bashed in a hostel in Melbourne's CBD and left in a pool of blood says she thought her attacker was going to kill her.

Carole, 28, was violently assaulted by a man who is believed to have stayed at the King Street hostel about a month earlier.

The man, on a working holiday from Belgium, had left Melbourne Connections backpackers on King Street on August 2 after he had punched and kicked another random guest over a squeaky bunk bed.

Hostel staff say he returned to the backpackers on August 28 at 3.30am, slipping through a security door that had been left opened, most likely by a guest who had gone outside for a smoke.