Pompey are in line for a £1m windfall if Liverpool win the Premier League.
The News understands the Blues would benefit as part of the deal which took Glen Johnson to Anfield in June 2009.
Then-chief executive Peter Storrie brokered the £17m sale of the England right-back to Liverpool, where he penned a four-year contract.
Pompey are remaining tight-lipped over the details of that agreement, adamant it is not club policy to discuss contracts.
The topic has also been the subject of much social media talk, growing louder with every Liverpool victory.
The News, though, can confirm the existence of the clause, which entitles the club to what is believed to be around £1m should the Reds lift the title while Johnson is still registered as their player.
At present, Brendan Rodgers’ team are two points clear at the Premier League summit with six matches remaining in the campaign.
However, third-placed Manchester City are four points behind with two matches in hand – making themselves the biggest threat in the chase.
Regardless, over the next six weeks the Fratton faithful will be urging Johnson and Liverpool on for their first title success since 1990.
Although, Pompey chief executive Mark Catlin has refused to be drawn on what is a mouthwatering financial prospect.
He insisted: ‘We will not be commenting on rumours.
‘Contracts remain private and confidential and that should never change.’
Now aged 29, Johnson established himself as a massive Pompey favourite following a shaky start and made 100 appearances, scoring four goals.
He initially landed on a season-long loan from Chelsea for the 2006-07 campaign and signed permanently the following year.
During his Fratton Park time, Pompey won the FA Cup, finished eighth in the Premier League, competed in Europe for the first time in the club’s illustrious history and took part in the Community Shield.
Johnson was a key figure during those memorable times, re-establishing himself as an England international in the process.
With owner Sacha Gaydamak pulling funding and banks calling in their loans, he was sold in the summer of 2009 having been crowned The News’ player of the year following an outstanding personal campaign.
As part of the £17m fee paid by Liverpool, Chelsea were entitled to receive around £4m from a large sell-on clause.
But, crucially, Storrie pushed for added incentives to benefit Pompey during those Anfield negotiations.
The chief executive was a stickler for putting in such clauses, although had no input in the infamous Asmir Begovic sale.
Now, almost five years later, the Blues could cash in.