Thieves targeted the Tigers, who are currently at the top of the Super League, in raids on Friday and Saturday at the club’s Wheldon Road stadium, police said.
Burglars broke into the Mend-a-Hose Jungle in the early hours of both days and escaped with money from offices and a safe.
Police said a large amount of damage was caused to the offices during the burglaries on June 30 and July 1.
Detective Sergeant Phil Davis, of Wakefield District CID, said: “Significant amounts of cash have been stolen form the club in two break-ins during the weekend and we are working closely with the club to identify and catch those responsible.
“The rugby club is a huge part of the community in Castleford and I would ask anyone who has information about this attack on it to come forward.”
West Yorkshire Police believe the raiders could attempt to dispose of their takings by depositing large amounts of coins in slot machines or at banks.
Det Sgt Davis added: “In particular, we are keen to speak with anyone who might have seen persons trying to cash in significant amounts of coins locally, given that thousands of pounds worth of coins were stolen.
“This could include persons trying to use automatic coin chasing machines, or even going into money brokers and local banks.
“Anyone who can assist is asked to contact Wakefield District CID on 101 referencing crime number 13170301178. Information can also be given anonymously to the independent Crimestoppers charity on 0800 555 111.”