The brothel was discovered by police officers acting on community concerns in Upperthorpe.
Officers who visited the property found a trafficked 42-year-old woman from China ‘who appeared to have been coerced against their will under false pretenses’.
The woman is now being supported by specialist agencies.
South Yorkshire Police said work is under way to establish who was behind the brothel.
The force said: “No arrests have been made yet, but enquiries are ongoing.”