Pompey will bank a windfall should Adam Webster move to the Premier League next month.
The central defender has impressed for Championship Ipswich since leaving Fratton Park in the summer.
Those displays have prompted him to be linked with moves to Sunderland and, more recently, Everton as clubs prepare for the opening of the January transfer window.
Should there be such an outcome for Webster, the Blues will also benefit, courtesy of a sell-on clause.
The 21-year-old earned Pompey £750,000, plus Matt Clarke, in the June 2016 deal which saw him signed by Tractor Boys boss Mick McCarthy.
However, it is understood a sell-on clause worth around 20 per cent was also negotiated by Blues chief executive Mark Catlin.
That equates to 20 per cent of any profit Ipswich make on the £750,000 they paid for Webster.
The sell-on clause is similar to the one inserted into the £800,000 transfer which took Jed Wallace to Wolves in May 2015.
Wallace is currently out of favour at Molineux, despite last month’s arrival of Paul Lambert as manager.
As for Webster, his star is rising as he continues to shine at Portman Road.
The youngster has so far made 19 appearances, scoring once, to establish himself at the heart of Ipswich’s defence.
Tractor Boys fans, though, have become frustrated over the lack of a promotion challenge this season, with the club currently sitting 16th.
However, Webster’s form has represented a massive positive for the Portman Road club.
On Boxing Day, Ipswich suffered a 2-0 home defeat to Fulham, with the defender featuring for the full 90 minutes.