The 36-year-old Icelandic international, who joined Pompey after leaving Charlton in summer 2007 and has since made 94 appearances for the club, made his comeback in recent weeks featuring as a late substitute in the recent Championship victories over Hull and Nottingham Forest as well as playing 90 minutes for the reserves against neighbours Havant and Waterlooville on Monday.
However, Hreidarsson said that when he suffered the injury against Tottenham in March he thought he had played his last game.
He told the News: "When it happened at Spurs I felt a bit sorry for myself for about two hours. I've been lucky throughout my career with injuries, but at that moment I thought that had been my last game.
"It was a nasty injury to be fair, a career-ending injury, so it looked like the end. I definitely felt a bit sorry for myself. Then I thought 'do you know what, it's not going to end this way'. At that moment I decided I was going to do everything in my power to make sure I would be back out there and playing football again.
"The reward was so big to me just to make it back. Luckily it has gone right so far and now it's a matter of getting a few more cobwebs out. It's such a privilege playing football, I still have a lot of passion for the game and I will keep going until the legs fall off me."