Detectives have until around midnight tonight to question a woman held on suspicion of attempted murder.
The 21-year-old was arrested after a man sustained life-threatening injuries in an attack.
Police have been standing guard outside the flat where the attack happened in the early hours of Saturday morning in Timpson Road, Fratton.
A 25-year-old man is fighting for his life in Southampton General Hospital.
The woman was arrested on Sunday on suspicion of attempted murder.
Officers can apply to extend the period of time they have to question her.