The grandfather said the Muslim "preacher" only said he would have a talk with the grandson to convince him to return to the family home.

He repeatedly denied telling Riza Morinaj he'd obtained permission from his grandson for the Hijama which involves using suction cups to draw blood and incisions made with a blade.

"I had no knowledge of this word 'Hijama'," he said on Friday at Morinaj's District Court trial.

The 39-year-old Melbourne man has pleaded not guilty to kidnapping in company with the intention of gaining an advantage occasioning actual bodily harm at a Sydney house in November 2016.

The grandson, who cannot be identified, has testified he was held down on the bed when suction cups were placed on him and incisions were made with a blade.

He said he was in pain, struggled and called for help and was told black blood would come out which was "the evil".

Under cross-examination from Morinaj's barrister, John Selimi, the grandfather said he was at the staircase near the open door of the bedroom when his grandson, Morinaj and two other men were inside.

He said he heard the reading of prayers from the Koran but no shouting or cries for help.

"At no stage did you hear (the grandson) calling out 'stop'?" Mr Selimi asked.

"If I heard that I would have rushed myself in the room and stopped it," he replied.

The grandfather said the only permission he sought from his grandson was for some men to talk to him.

The grandson testified he and his wife moved out of his parents' home as she felt she was being treated like a slave - but his relatives believed his in-laws had put black magic on him.

The grandfather repeatedly denied Mr Selimi's suggestions that he had asked Morinaj to perform the Hijama and had told him his grandson gave permission for it to take place.

He also denied knowing that Morinaj had a "vast degree of expertise" in performing Hijama saying he'd never talked to anyone about the practice.

The trial continues before Judge Helen Syme

Australian Associated Press