The blade was plunged through his hand, slicing through a main artery and causing the 31-year-old to bleed heavily.
Paramedics were called to the scene of the attack on a top-floor landing of La Collette Flats in Green Street at around 4.30 am.
The man is today still being treated at the General Hospital.
His injuries are not life-threatening and he is expected to make a full recovery.
