Middlesbrough are reportedly set to sue the English Football League for their failure to enforce financial rules regarding Derby County's purchase of Pride Park.
The Times have claimed Middlesbrough have sent a legal letter to the EFL headquarters.
Nottingham Forest's arch-rivals finished in sixth place last season, taking the final play-off spot from Boro, who finished one point behind them in seventh.
That denied Middlesbrough, then managed by Tony Pulis, a chance at promotion to the Premier League and a £180m windfall that would have followed, had they beaten Leeds United and Aston Villa.
This ongoing saga is showing no signs of drawing to a close.
Middlesbrough owner Steve Gibson has been outspoken about clubs using a loophole to purchase their own stadium. Rivals have accused Derby, Sheffield Wednesday and Reading of doing this in the last year.
Boro chief Gibson has previously explained: “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 and needs to be followed and if it’s not followed sanctions must be taken against those clubs that cheat.”
In the Rams' case, owner Mel Morris is claimed to have purchased Pride Park using a separate company for £80m, as seen in the club's latest accounts, with a deal to lease the ground back to the club.
However, at the time of purchase, the ground was listed on the club's assets as valued at £41m, which has sparked the EFL to launch an independent investigation on the stadium's value.
This year Derby posted a profit of £14.6m pre-tax, which eased concerns that they would fall foul of the EFL's Financial Fair Play regulations, which state clubs cannot lose more than £39m in three years.
