Leeds have been ordered to pay an £18million bill after losing their Court of Arbitration (CAS) case over the transfer of Jean-Kevin Augustin.
The French striker joined Leeds from RB Leipzig on loan in January 2020, and would only make three appearances before returning to the Bundesliga club.
However, the deal included an obligation to buy him permanently for €21m (£18m) if they were promoted to the Premier League - something which they achieved.
Leeds though felt that the loan, and its conditions expired on June 30 of that year - before they were able to achieve promotion due to the Covid-delayed season.
Leipzig disagreed and a FIFA hearing in June 2021 upheld the Bundesliga side's claim and said Leeds had to pay the transfer fee, with a first installment of €6.7m (£5.85m) due.
Leeds appealed the decision but have lost their CAS case - though they are set to launch another appeal.
The ruling means that Leeds would fork out a hefty amount on a player they never permanently owned.
A statement by the Court of Arbitration, as per the Athletic said: 'The panel held that the 'Purchase Obligation' had been triggered at the end of the 2019-2020 season, even though the season had concluded later than expected due to the disruption caused by the outbreak of the COVID-19 pandemic, and confirmed the 'Challenged Decision' in full, including the obligation of LUFC to pay to RB Leipzig the first instalment of the transfer fee, the two other instalments being not due yet, at the time of the FIFA procedure.'
Leeds released a statement in the aftermath of the verdict in which they said they would carefully review all their options with a view to appeal.
In the statement they said the ruling 'contradicts' FIFA regulations in view of the unique impact left by the Covid-19 pandemic.
They said: 'Leeds United are surprised and disappointed by the Court of Arbitration for Sport’s decision, which not only contradicts the language and meaning of the contract but also the practices adopted in European football under FIFA regulations, due to the unique impact of the extensions to the season necessitated by Covid postponements.
'The club will now review carefully all of its legal options with a view to an immediate appeal. We will make no further comment at this time.'
Augustin was drafted in at the halfway point of the Whites' 2019/2020 promotion bid after Arsenal's winter recall of striker Eddie Nketiah midway through a season-long loan spell left the Elland Road outfit needing a replacement.
When he arrived, Augustin was not adequately fit the meet the needs of Marcelo Bielsa's team, and only made three brief substitute appearances before a hamstring strain ruled him out of contention.
After Leeds decided not to bring him to Elland Road after their promotion, he instead ended up joining French side Nantes on a free transfer in October 2020.
He would only go on to make ten appearances in two seasons before he joined Basel in the summer - scoring three goals in nine appearances since the move.
RB Leipzig in their own statement on the matter said: 'This decision of the CAS is in principle final.
'Although Leeds United has the opportunity to lodge an appeal with the Swiss Federal Supreme Court, the procedural hurdles for doing so are very high and no points of attack against the CAS decision are to be expected.
'The outcome of the proceedings is therefore fully in line with RB Leipzig’s intentions.'