The scrum-half will also have to sit out England’s Test against New Zealand in Denver in June after fracturing his kneecap.
Gale suffered the injury in last Friday’s win over Wakefield Trinity and underwent surgery today.
Castleford assistant coach Ryan Sheridan admitted: “It is a massive blow as he is a key player for us - an international half-back.
“He took a whack in that game and it seemed fairly innocuous.
“He played for most of the half but had to come off at half-time.
“It’s looking like something like three months but we’ve got a good physio in Matt Crowther and Galey will be meticulous in his rehab and getting himself right as he’ll want to be back as soon as possible.
“Fingers crossed it’s sooner rather than later.
“Obviously it’s devastating news for him and for us but we're a good team and we have players who can fill in and accommodate until he gets back fit.”
Castleford visit Hull FC on Saturday when they are also without Samoa stand-off Benny Roberts.
Jamie Ellis will fill one half-back slot while hooker Paul McShane could fill in alongside - as he did so admirably against Wakefield - or even prop Grant Millington.
Sheridan added: “It’s a good opportunity for Jamie to nail a spot down and become a dominant half for us.
“We’ve got young Jake Trueman, Paul McShane and Grant Millington can play there as well so we have some cover and options.
“We might have to play a little bit different but we’ll spread the responsibility across the team and it’s a good challenge ous as a team and as a staff to put a plan together.”
Teenager Trueman arrived as a half-back but has been impressing at full-back of late.
Winger Greg Eden could play full-back but he, too, is currently injured.
Sheridan admitted: “Truey’s doing a good job at the minute.
“We have got options there when we get a few players back in terms of our halves and backs like when Greg gets back.
“But we just have to settle our halves down over this period of Galey missing and get our combinations right.”
Jy Hitchcox may come back into contention for the wing shortly with his loan spell at Bradford Bulls soon to end.
Sheridan added: “Potentially that could happen.
“We’ve had to move Michael Shenton and he’s a world-class centre playing on the wing.
“Players are prepared to do whatever’s the best for the team. But ideally we'd like Shenny back in the centre until we get Greg back so there is potential for a wing spot being available.”
Gale played in the World Cup final for England alongside Warrington's Kevin Brown who has since announced his international retirement so Wayne Bennett will need a new half-back partnership versus the Kiwis in America.
That should see Gareth Widdop and Wigan's George Williams paired together - and perhaps open up the door for a return of Sam Tomkins, too.