Middlesbrough are preparing to take legal action against the English Football League over claims that it did not enforce its financial rules over Derby's stadium.
The PA news agency understands Boro are planning to sue the governing body over what they believe to be a loophole in the regulations that has been exploited by several clubs.
Derby, who finished a point ahead of the Teessiders to deny them a place in last season's Sky Bet Championship play-offs, did so after owner Mel Morris used another of his companies to buy Pride Park for £80million, reported to be almost twice the £41million value listed on the club's books, and then lease it back to the Rams.
As a result, they were able to post a pre-tax profit of £14.6million and avoid sanction under EFL profit and sustainability rules which prevent clubs from making losses of more than £13million a year over a 36-month period.
Boro were not commentating on a report on Friday which claimed they are to sue the league over the matter, although sources on Teesside confirmed legal advice has been taken.
An EFL spokesman said: "We do not comment on the financial circumstances of specific clubs."
For his part, Morris is adamant his club have committed no offences, telling talkSPORT: "We've done nothing wrong. We're very comfortable with what we've done. The valuation, in our opinion, was fair and reasonable.
"We didn't use a loophole. Let's be very clear on this, there is no loophole here. The rules are extremely specific on this, that the sale of a fixed asset is allowable. It's a single sentence. It is allowable."
Boro chairman Steve Gibson has been an outspoken critic of clubs he alleges have spent beyond their means and yet not been sanctioned, as Birmingham were last season when they were docked nine points after recording a loss of almost £10million in excess of the limit.
Speaking as new head coach Jonathan Woodgate was unveiled in June, he said: "If the rule is not going to be followed, don't have it, and if the rule is there...
"If we have have a centre-half who picks the ball up in the penalty area, I don't expect the referee to ignore it. If a player deceives the referee, I don't expect that to be ignored, and I don't expect the EFL and other clubs to ignore Financial Fair Play.
"It's there, it's a rule, it's an important rule, it needs to be followed and if it's not followed, sanctions must be taken against those clubs that cheat."
Asked what the solution was, Gibson replied: "That lies with the EFL. We're just Middlesbrough, we're a minnow in this. The EFL and the other clubs have got to act against it."