Derby County’s lawyers are preparing a response after Middlesbrough mounted a legal challenge, questioning the validity of Derby’s decision to sell Pride Park to the club’s owner.
Middlesbrough told Derby they were planning to sue on Friday - three days before the play-off final at Wembley against Aston Villa.
Derby recorded a pre-tax profit of £14.6m after selling their Pride Park stadium to owner Mel Morris for £80m, before leasing it back.
Boro are adamant that Pride Park is not worth the £80m owner Mel Morris paid for it, and that the sale was solely an attempt to side-step the EFL's financial rules.
Sky Sports News has been told that Derby are bemused by Boro's complaint, saying they cleared the stadium sale with the EFL before the deal was done, and they remain convinced it is within the rules.
They also had the stadium independently valued before the sale, and are currently investigating whether they can put a roof on Pride Park, to make it more commercially viable outside of match days.
Sky Sports News has seen two emails, sent to Middlesbrough by Derby's bosses, inviting officials from the North East to come and view Derby's financial accounts. Boro did not reply to either offer.
The Rams finished just two points above Middlesbrough in the Championship, securing the final space in the play-offs, before eventually losing 2-1 in the final to Aston Villa at Wembley.
It is likely to be a real source of conflict when officials from Derby and Middlesbrough sit alongside each other in Portugal next week, during the EFL's end of season AGM.