Balram Chainrai and Levi Kushnir were entitled to £3m should the Blues reach the Premier League by June 30, 2023.
However, that is now not possible within the stated time frame after Danny Cowley’s side finished 10th in League One this campaign.
Portpin’s stipulation formed terms which involved the fan ownership takeover of Pompey in April 2013.
The sale was agreed following an emotional two days at the High Court, during which the Blues were under threat of liquidation and having their Football League membership withdrawn.
However, Portpin eventually reached an out-of-court settlement with administrators BDO, thereby allowing the Portsmouth Supporters’ Trust to, initially, become majority owners.
Portpin were paid £3m for Fratton Park – while also stood to benefit by an additional £3m should Pompey return to the Premier League within 10 years.
The Blues began their assent by claiming the League Two title in May 2017 under Paul Cook, yet have since stalled.
During the last five seasons in League One, they have twice reached the play-off semi-finals, while finishing eighth, ninth, and now tenth.
It means that even should they win promotion to the Championship next term, it will not be possible to reach the Premier League in time for Portpin to benefit.
Before the April 2013 High Court case, Portpin held a disputed charge of Fratton Park and demanded £17.4m for its sale, which included money they claimed was owed.
Alternatively, the club were offered the chance to pay £100,000 a month – totalling £1.2m a year – to rent it from Portpin.
Pompey have since been sold to Tornante in August 2017, who are currently overseeing a £11.5m redevelopment of Fratton Park.
Meanwhile, in the 2019 documentary Our Club, a rare interview with Chainrai saw him claim he ‘decided to let go’ of Pompey for the ‘betterment’ of the club.
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