The club has debts of about £60million and have had four owners just this season.
Pompey will be docked nine points as a result of going into administration.
Administrator Andrew Andronikou will now be responsible to start cutting costs at the club.
Former Portsmouth chairman Milan Mandaric told BBC Midlands Late Kick Off: “It’s really sad. It’s not right, it’s not fair to those people there and I just hope for the sake of the club, and the sporting community, and football in that city, they sort things out.
“And I think they eventually will. That club will never die. That club has a lion’s heart. They (Portsmouth fans) love their club, they will always be there. Unfortunately they don’t deserve these kinds of difficulties.”