The firm took a haircut on the value of the non-operating licence in order to secure Competition Commission clearance for the deal to buy 19 gaming establishments from Coral.
The charge emerged in annual results which showed Rank, also the owner of Mecca Bingo, recorded a 7% rise in annual revenue from £584.3 million to £625m.
Adjusted pre-tax profit was at £65.1m for the 12 months to June 30, down 1% on the previous year's £65.7m.
Rank said it expects to complete the acquisition of five non-trading casino licences around the UK, including one in Glasgow, from Clermont Leisure (UK) by the end of this month in a deal worth around £6m.
It is also planning a refurbishment of its Merchant City casino in Glasgow as part of a £9.4m investment programme.
In total, the Grosvenor Casinos division saw its revenue rise from £261.5m to £300.3m, bingo arm Mecca was up from £293.6m to £296.2m and European operation Enracha dipped from £29.2m to £28.5m.
Rank said it has abandoned a bingo hall refurbishment initiative, launched four years ago, to attract younger players to its bingo halls after saying results were disappointing.
The "Full House" concept was designed to attract a new and wealthier audience to the game after Mecca, which has 13 of it 97 sites in Scotland, was knocked by the smoking ban and gambling legislation.
But it has failed to stem the ongoing decline in bingo customer visits, with Rank admitting its investment in the conversions had not paid off. It spent £700,000 each to revamp bingo halls in Hartlepool and Knotty Ash, Liverpool in the last year and has seen improved performance.
"However, the Full House Destination estate performance as a whole has been disappointing and the capital invested has not improved the public's perception of bingo sufficiently to address the general decline in admissions," the group said.
"Due to the inadequate return on investment from these conversions, the group will not be committing to any further at this present time."
Nine Full House venues have been opened since they were launched in 2009.
Rank is Britain's largest casino operator, with 55 venues including in Glasgow, Edinburgh, Dundee and Aberdeen.
Total customer visits were up and with spend per visit increased 7%, mainly driven by high rollers playing at London venues.
The warmer weather since the end of June has also had an impact on trading, with Rank saying like-for-like revenue is down.
Analysts at Panmure Gordon predicted Rank's pre-tax profits for the coming 12 months would be more than £71m and kept a hold rating on the stock.
The shares closed down 2.5p, or 1.5%, at 158.5p.