Rangers earned three times what they should have from Everton, according to a football finance expert.
Data analysts Twenty First Group have released a report on the financial window and they claim it proves the Toffees overpaid for the Scotland star.
The calculate the wroth of players using a valuation model.
Patterson made the move from Ibrox to Goodison last month for an initial £12million fee, which could rise to £16million.
The 20-year-old is regarded as one of the best young right-backs in European football, but was understudy to Rangers captain James Tavernier.
Patterson has yet to make his Toffees debut although boss Frank Lampard insisted he's been impressed with the youngster.
Omar Chaudhuri, the Twenty First Group's chief intelligence officer, claimed Patterson is worth closer to £4 million.
He said: "Everton's purchase of Nathan Patterson reflected the club’s own estimations of the Scot’s potential. Our model valued him at €5m (£4M), far below the reported €14m (£12M) paid.
"Patterson had played less than 600 professional league minutes for Rangers, and while expectations are high it is rare to see such inexperienced players transact for such sums."
