Massimo Cellino’s reign as Leeds United owner is under serious threat after an Italian judge ruled he set up a “bogus corporate screen” as part of a “Machiavellian simulation” deliberately to evade paying import tax on a yacht in 2012, meaning the Football League could bar the Italian from controlling the club.

The former Cagliari owner took control of Leeds in April this year through his company Eleonora Sport after an independent QC overturned an original decision to block him from buying the Championship side because there was insufficient evidence that he acted “dishonestly” when failing to pay nearly €390,000 (£305,000) import duty on his private boat, the Nélie.

However, the full written ruling on the case – seen by the Guardian – states that there was “no doubt as to the existence of an elusive intent on the part of [Cellino]”. Sandra Lepore, the Sardinian judge who handed Cellino a first-grade criminal conviction in March, reported in a six-page document that the businessman used a United States company called Freetime Miami LLC in order to buy the yacht and avoid paying import duty on it in Italy.

Cellino’s position as Leeds owner could therefore be in jeopardy as the Football League’s owners’ and directors’ test disqualifies individuals who “have unspent convictions for offences of dishonesty”. Commonly known as the fit and proper persons test, the League has these rules in place to prohibit those individuals from being directors, 30% owners or from exercising control of clubs.

The League has yet to obtain the full written reasons in the Nélie case from judge Lepore but, given that it initially blocked Cellino’s original attempt to buy Leeds earlier in the year, it could move to bar him from ownership once more, even though the Italian has appealed against the original, first-grade conviction in Sardinia.

Judge Lepore rejected the argument by Cellino that his vessel worth around €1.85m was covered by the European Union’s temporary importation procedure when it was searched by authorities in Cagliari in 2012. That rule allows for non-EU flagged yachts used by non-EU residents to be brought into European waters for up to 18 months without being subject to customs duties or VAT.

Cellino also argued that he had been prevented from having the Nélie sailed back to the US because of technical problems, which he was in the process of having repaired. However, judge Lepore said these claims were “completely unproven”.

She wrote: “There can therefore be no doubt as to the existence of an elusive intent on the part of [Cellino], as it must be held that the evasion of the import VAT was the result of a Machiavellian simulation, put in place by the aforementioned [Cellino], in order to disguise a definitive admission [of the yacht] as a temporary admission.”

Regarding the registration of the Nélie by the Florida-based company Freetime Miami LLC, Lepore added that it “leads us to believe, beyond any reasonable doubt, that the real owner of the Nélie yacht is Massimo Cellino himself and that Freetime Miami LLC is nothing but a bogus corporate screen formed in an ad hoc manner in order to allow [him], the effective user of the asset, to bring into EU territory a means of transport as part of a temporary importation procedure, thus eluding the payment owed in import duty”.

Giovanni Cocco, Cellino’s lawyer in Italy, strongly attacked Lepore’s report, saying: “That document is unpresentable. It is full to the brim of errors of merit and of law. It does not take into account what emerged in the trial – that is to say, that nothing implicates Cellino. I have already … lodged an appeal and have also completely demolished the [judge’s] reasoning.”

Cellino is also accused of evading import duty on assets in two other cases with hearings scheduled for next month in Cagliari. One concerns a Land Rover and the other another, smaller, yacht, named Lucky 23. He denies the charges.

Cellino has maintained his innocence throughout the Nélie case and has appealed against the original first grade conviction. Under Italian law, which allows for repeated appeals, it is not considered a definitive conviction. One issue of contention is whether Cellino is officially a resident of Cagliari or Miami.

The new Leeds head coach, Darko Milanic, was officially unveiled by the club but the club’s future has once again been cast in doubt. The Football League chief executive, Shaun Harvey, previously chief executive at Leeds under Ken Bates, said earlier this month that the yacht case was still a “cloud hanging over” Cellino and the League, adding: “It’s exceptionally disappointing that we haven’t actually had the judgment.”

Judge Lepore completed her report at the end of July.