Viktor Gyokeres is a ‘nightmare’! How Arsenal are unlocking full potential in striker that could cost them another £3.5m before end of the season

However, Gyokeres made a slow start to life at Arsenal, scoring just five goals in his opening 21 league appearances, three of which came against promoted pair Leeds and Burnley. Many were quick to criticise the 27-year-old, with a number of football fans dubbing the striker to be the worst signing of the season.

The forward, though, has started to show his best form having scored five goals in his last five Premier League outings, including a brace in last weekend's 4-1 north London derby win over rivals Tottenham. Gyokeres bagged a second half brace in what was arguably his best performance of the campaign for the Gunners.

And Arteta now believes that Arsenal are on "the right trajectory" to unlocking Gyokeres' full potential.

Speaking on Friday, ahead of Sunday's welcome of London rivals Chelsea, Arteta suggested there is more to come from Gyokeres following his two-goal salvo on Sunday. "I think one thing leads to another," Arteta began. "When you score the first one or the performances are good, you have more time with your team-mates, you understand the games, the opponent, the league better. Everything helps.

"We know his qualities. He is undoubtedly an incredible striker. We need to feed to his quality, we need to understand him better, he needs to understand the team, the league better, I think we are in the right trajectory."

And when asked if Gyokeres had struggled with confidence, Arteta replied: "That's a question for him. Obviously I know the demands he puts on himself, the expectation that he has to help the team and I am confident because a lot of the times, our defenders, when they have to train against our players, [you ask], 'How do you feel when [you face him]?' and [they say], 'It's a nightmare'.

"That's a really good way to understand the quality of a player or how it is to defend him."

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.

Arsenal's lead at the top of the Premier League table may be cut to two points by the time they take on Chelsea on Sunday. Rivals Manchester City face Leeds on Saturday evening as the Cityzens look to keep on the coattails of the Gunners in the title chase.

The Gunners welcome the Blues on Super Sunday and will be confident of claiming a result against their London rivals. Indeed, Arsenal are unbeaten in their last eight meetings with Chelsea, winning five, but Arteta insists that the recent head-to-head record "doesn't change the preparation" ahead of their huge game this weekend.

"What we've done two weeks ago or two years ago is irrelevant, because every game and context is different. The players might change, the mood of the teams can be in a different state or what is at stake is different, and we are prepared," the Spaniard said.