Denny Solomona has been registered to play in Sale's Champions Cup squad

Sale Sharks appear to have signed Denny Solomona after registering the player in their Champions Cup squad.

The 23-year-old Samoa international remains contracted to Super League club Castleford, for whom he scored a record 42 tries in 2016, but he failed to report for pre-season training in November and is thought instead to have linked up with the Sharks.

The RFL says Solomona joining Sale would be hugely worrying for their sport. "This has profound implications for the game," Nigel Wood, RFL chief executive said.

"Clearly the sanctity of contracts have to be respected. It's a concern for more than the game, it's bigger than just rugby league or rugby union, it's almost like a law of the land issue really.

Solomona scored 42 tries in Super League in 2016

"Unilaterally walking away from things is not something you would condone. We've been in contact with both the RFU and Premier Rugby to express our concerns. They are aware of our position."

Sale have made no official comment since director of rugby Steve Diamond confirmed his club's interest in the player, claiming he had resigned from rugby league, but are thought to be close to announcing his capture.

Along with former Wigan and England winger Josh Charnley, Solomona has been added to Sale's Champions Cup squad ahead of Saturday's round-three match against Saracens at Allianz Park, with Nick Scott and Will Addison being unregistered.

Castleford are ready to take the matter to the High Court for a case that could have major ramifications for rugby league.

The Tigers, who say they rejected three offers for a player who has two years left on his contract, have appointed leading London barrister Nick Randall QC - whose other clients include England captain Wayne Rooney - and Leeds-based sports lawyer Richard Cramer to fight their case.

Solomona, who left Melbourne to join London Broncos in 2014, was named in the 2016 Super League Dream Team and short-listed for the Man of Steel award after breaking Lesley Vainikolo's record of 40 tries in a Super League season this year. He made his Samoa debut in an international against Fiji in October.