Castleford are seeking damages of £500,000 from the player, his agent Andy Clarke and Sale after claiming the prolific New Zealander purposely broke his contract to make the cross-code switch.
According to lawyers acting for Castleford, Sharks have refused to pay anything to the West Yorkshire club for the 23-year-old, who was under contract until 2018 but refused to return for pre-season training in November and made his Sale debut last month.
Castleford are taking matters to the High Court and have lodged documents at Leeds District Registry which outline their case including a raft of revelations.
Sale, in response, are taking legal advice.
In their revelations, Castleford claim to have already turned down a £150,000 offer from Sale - rising to £200,000 if other conditions were met - in August, insisting the player was not for sale.
The documents show that Sharks duly withdrew their bid but Diamond sent the following email to Castleford chief executive Steve Gill on September 8.
It reads: “Since we last spoke, Denny’s agent has informed me that Denny has spoken to yourself and your Chairman and said that he doesn’t want to play Rugby League any longer.
“After being informed of this, legal advice has been sourced and we are confident that when he walks away he will be free to play Rugby Union. Our advisors also said that any claim for damages that you may have will be significantly lower than the £150,000 previously offered and that is why we withdrew that offer.
“I am told that whilst you should be compensated for any breach, the courts won’t just award the amount you say is required to replace Denny…
“I, however, do not want to get the lawyers involved, it isn’t our style and it will be a distraction as well as expensive to go through the courts for the next two years and you will not receive any cash for that period. Therefore, the club are prepared to pay immediately £50,000 and you will release Denny from his contract at the end of September after your last match.
“Hopefully you will see the sense in a quick quiet deal and allow you to recruit alternatives.”
Castleford argue Sale and Clarke entered into a “cynical calculation that they would be better off by procuring the player to breach the contract with Castleford Tigers rather than negotiate a transfer fee to secure a lawful release”.
Solomona’s contract was £49,000 last season, rising to £60,000 this year and then £70,000 in 2018, the final year of his deal.
Castleford say in May last year, the player’s previous agent asked for £95,000 per year and/or a new contract.
Later that month, the club adds, Solomona – who ended as Super League’s top try-scorer and broke Castleford’s club record with 42 – texted Gill to say he wanted nothing less than £100,000 and that Clarke was now his agent.
Clarke, according to Castleford, also asked for his agent’s fees of five per cent per cent but with a break clause that after two years, the player could leave for union.
When the club refused to budge on the latter two, in a resignation email to Gill on September 27, Solomona said he felt “insulted, undervalued and treated like a piece of meat to be traded.”
Castleford, who turned down an approach from Warrington Wolves in August, rejected his resignation.
However, they argue Solomona’s subsequent non-attendance at the start of pre-season training on November 7 allied with social media images - a video of him playing table-tennis with Sale players the following day and a picture of a Sharks removal van outside his home - proved a “clear unequivocal repudiatory breach of contract.”
Tigers, therefore, terminated his deal and began their claim for losses and damages arising from that breach.
Documents also show that Castleford loaned Solomona £5,000 in November 2015 - to be paid back in 12 monthly instalments - and the same sum again in January last year.
They say £8,500 remains outstanding while the outstanding cost of Solomona’s contract is in the region of £130,000.
The club says it could not secure a like-for-like replacement and had to “re-order” their squad as a result of the former Melbourne Storm player’s actions.
They brought in Zak Hardaker from Leeds Rhinos but not as a direct replacement and say the total cost of signing the England full-back until November, 2018 - when Solomona’s contract was due to expire - is likely to be around £585,000.
Castleford argue, then, that their losses suffered are £455,000 and they contend that a genuine transfer value for Solomona would have been £500,000.
When asked about the comments, on behalf of Sale and Solomona, Diamond told The Yorkshire Post: ‘Everything is in the hands of our lawyers and they are dealing with it.”
Clarke was contacted for a comment but did not respond.