The 22-year-old woman had approached Althaf Hussain, a Unani practitioner, who was running a clinic at Pudupet here, for an ailment.
Under the guise of helping her escape "from the spell of black magic," Hussain had allegedly beaten up the victim and sexually assaulted her after taking Rs 8000, police said.
Hussain threatened the woman that her family members would be eliminated if she revealed what had happened, police said.
Investigations revealed that Hussain had earlier sexually assaulted another woman in Vepery and the victim had poured acid on him.