The defender was stretchered off during his side's 3-1 victory over Stevenage in the FA Cup after going over on his right ankle.
Speaking to reporters on after the game, manager Harry Redknapp immediately showed concern.
"Looking at his injury, it would be a miracle to think he is not [out for the season]. It's long term for sure," said Redknapp.
He went on to describe it as a "real bad injury. It is his ankle and knee. He has gone off to hospital - it wasn't good."The extent of the injury has now been confirmed by the club, with Dawson now looking doubtful to figure in England's Euro 2012 squad, much to the disappointment of both player and manager.
Redknapp added: "It’s a big blow for Michael. He’s a great guy, fantastic professional. You want Michael in the team and around the place."
The injury leaves Redknapp short on defensive cover, with only Younes Kaboul and Ryan Nelsen fully fit and able to play in the centre of defence. William Gallas has only just returned from a calf injury, whilst Ledley King remains a doubt due to his chronic knee problems.
Team-mate Emmanuel Adebayor sent his condolences via Twitter.
"Sad news re Michael Dawson.Wish U speedy recovery mate.We're going 2 push hard for u for the rest of the season and hope 2 bring home FA Cup"