Watts, 23, suffered a knee ligament injury during last week’s pre-season friendly against Featherstone.
Head Coach Lee Radford said: It’s obviously disappointing for us and especially Liam who is a big part of our pack.
“His presence will be missed, but it presents another opportunity for another of the players.
“The likes of Josh Bowden have worked hard in pre-season and are desperate for a chance so it’s up to them to earn that spot and keep it now.
“Liam is in very good hands with our medical team and if they can get him back in six weeks or so then they’ve done a fantastic job.”