The Hawks have missed out on a windfall following Nigel Atangana’s Leyton Orient switch.
The midfielder left Pompey last week in a 18-month deal believed to be around £20,000.
With the Blues willing to allow him to depart for nothing upon the expiry of his contract in the summer, the fee was warmly welcomed.
However, the sum was not high enough to trigger a sell-on clause to benefit their non-league neighbours.
The Hawks sold Atangana to Pompey for an undisclosed fee in the summer of 2014.
As part of that arrangement, they were entitled to a percentage of any future profit made on the Frenchman.
However, the £20,000 collected fell well short of the original outlay.
Hawks director Trevor Brock said: ‘As ever, we included a sell-on clause in the Atangana deal.
‘This covered anything made in excess of the transfer fee Portsmouth paid.
‘We have a confidentiality agreement with them so cannot reveal that fee.
However, it was considerably in excess of what Leyton Orient paid.
‘As a result, we won’t receive anything. Then again, sell-on fees don’t usually come to anything for teams at our level.
‘Still, it’s a great move for Nigel and, while I am quite surprised he didn’t make it at Pompey, I’m sure he will show what he can do.’
Meanwhile, the Hawks host Bishop’s Stortford tonight (7.45pm), with Jack Whatmough set to start.
Pompey season-ticket holders can attend the Westleigh Park game for £5.
HAWKS v Bishop’s Stortford preview n Page 44