Arsenal coughed up £54.8m ($74m) to sign Gyokeres from Sporting last summer, however a series of clauses could see that rise to £63.5m ($85m). At the end of the season, though, the Gunners could have already handed over an extra £3.5m in add-ons.
The Premier League leaders are close to forking out an additional £436,000, a fee that relates to the number of goals and assists Gyokeres registers for the north London side. Sporting are due that figure every time Gyokeres hits 20 goals and assists combined.
At present, the summer signing has 15 goals and two assists to his name after his brace against Spurs, meaning another three goal involvements would see Arsenal send £436,000 to Portugal. Sporting would be due the same amount should he hit a further 20 goal contributions, though that add-on is capped at £873,000.
Arsenal have already had to pay out £1.1m to Sporting after Gyokeres made 20 appearances of 45 minutes or more this season, with the total amount for that add-on capped at £4.4m. The striker needs to make 80 appearances for that full amount to be reached, and is 10 away from triggering another £1.1m payout, which means Sporting could be due a further appearance-related windfall before the season is out.
The third add-on relates to Arsenal qualifying for the Champions League, with Sporting due £874,000 each time the Gunners reach Europe's elite club competition. This, again, is capped at £3.5m.