When they sold Bale to Tottenham in 2007, they inserted a sell-on clause believed by Sky Sports to be 15 per cent of any future transfer fee.
However, when they found themselves in financial difficulty, Southampton waived that clause and agreed to receive around £1.5million plus Spurs youth keeper Tommy Forecast.
Forecast never made an appearance for Southampton and is currently without a club.
Saints can still expect a small percentage of a Bale sale to cover training costs - that figure is thought to be around two and a half per cent.
However, a potential sale that could have netted Southampton £13million will instead only yield around £2million.