Mason, 30, has been forced into rehabilitation after struggling to recover from the injury sustained in last week’s pre-season friendly victory at Wigan.
It means he will miss the Super League opener against the Warriors at the DW Stadium, and he joins David Fa’alogo (back), Larne Patrick (wrist), Luke O’Donnell (knee), Tony Tonks (suspended) and David Faiumu (shoulder) on the sidelines.
Head Coach Nathan Brown told the club’s official website: “Losing Keith is another big disappointment, particularly as it means we’re one more prop down, that obviously adds to the pressure on those who will be available.
“I am confident we’ll be able to field a formidable side when we go to Wigan next weekend. We’ve got back-rowers who can push up to prop and Michael Lawrence ready to come into the second row. Michael’s switch will free up Joe Wardle to slot straight back in at centre after he had to miss the Wigan trip with a hip injury.
“Bobby Fairbank has also been going well, and this could be the moment he’s been waiting for too. The injuries to the senior blokes do give some of the younger boys a chance to see what they’re made of.”
Mason, who opted to stay at the Giants despite reported interest from St Helens, is entering his sixth season at the Galpharm Stadium, having previously played for Saints, Castleford and Wakefield in Super League.