Shinawatra sold his stake in Manchester City in September 2008
Premier League boss Sir Dave Richards says any takeover of Portsmouth would be refused if former Manchester City owner Thaksin Shinawatra was involved.
UAE property tycoon Dr Sulaiman Al Fahim is close to assuming full control at Fratton Park within the next month.
But the south coast club have strongly denied reports claiming ex-Thai Prime Minister Shinawatra will play a role.
And Richards told BBC Five Live: "If Dr Thaksin was involved, the takeover will not be allowed to go through."
Newspaper reports also suggested Richards himself has been involved in the deal, but Portsmouth denied this.
Richards said: "At this stage the Premier League do not know if he (Shinawatra) is involved.
"The Premier League have met the advisors to Dr Sulaiman this week and we have made it very clear that we want to know who are the shareholders in the possible takeover of Portsmouth.
"Before it can be taken over the people who are involved have to meet the fit and proper persons test."
Earlier, Portsmouth released a statement on their official website denying any link with Shinawatra.
The statement read: "Neither Thaksin Shinawatra, nor his advisor Pairoj Piempongsant are involved in funding Dr Sulaiman al Fahim's bid for the club.
"A representative for Dr Sulaiman al Fahim met with Premier League officials last week and confirmed that he is the sole purchaser of the football club and this will be verified by his lawyers.
"Pompey executive chairman Peter Storrie met Pairoj Piempongsat during his time at Manchester City some two years ago. Pairoj subsequently introduced Mr Storrie to Dr Sulaiman al Fahim and that is the extent of his involvement in the proposed takeover."
As for suggestions Richards has a role in the sale, Portsmouth also said: "Sir Dave Richards has had no role to play in the proposed takeover, other than providing advice in his role as chairman of the Premier League.
"To suggest otherwise undermines the excellent work he does in his position."
The statement concluded: "The due diligence process for the purchase of the club is continuing well and should be completed by early July."
United Arab Emirates businessman Al Fahim was the initial figurehead of the Abu Dhabi United Group when they took control of Manchester City from Thaksin last year, but is now acting for himself.
His projected move for Portsmouth follows negotiations led by Portsmouth executive chairman Storrie on behalf of club owner Alexandre Gaydamak.
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