Dylan Voller, the 19-year-old whose treatment at an NT youth detention centre sparked a royal commission, is due to give evidence.
Mr Voller is now in an adult jail and will on Monday be taken to the Darwin Supreme Court to give the inquiry his version of events.
However, his mother Joanne and lawyer Peter O'Brien say the teen is concerned about giving evidence while still in custody and fears repercussions from prison guards.
The royal commission comes after footage screened in July showed Mr Voller and five other youths being tear-gassed and spit hooded at the notorious detention centre.
Mr Voller can be seen strapped to a chair wearing a hood in images which shocked many when aired by the ABC's Four Corners.
He is expected to front a closed session as the inquiry resumes on Monday.