Gyokeres was wanted by Manchester United and Arsenal on the back of a prolific season for Sporting, and it appeared the 27-year-old was on the verge of joining the Gunners.
But fresh reports in Portugal today claim the transfer is now on the brink of collapse because Arsenal and Sporting are still said to be struggling to agree a fee for the frontman.
The issue, claims Record in Portugal, is that Arsenal are offering a package of £56m plus future payments of £8.6m, but Sporting are said to be demanding £60m up-front and won't budge on that stance.
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Gyokeres has not reported back for pre-season training with Sporting having made clear his intention to join Arsenal.
What happens next is unclear at this stage, but could have a knock-on effect on the [Black Cats](http://www.thenorthernecho.co.uk/sport/football/sunderland).
That's because Sporting are said to have identified Almeira striker Luis Javier Suárez - who has been heavily linked with Sunderland this summer - as their ideal Gyokeres replacement.
Suarez is in-demand this summer after a stunning season in the Spanish second tier, in which he scored 27 goals and provided a further eight assists in 41 appearances.
With Almeira having missed out on promotion to La Liga, there's an acceptance at the Spanish club that the 26-year-old will be on the move this summer, with the striker said to be valued at around the £21m mark.
Reports in Spain claim Sunderland have tabled an offer for Suarez this summer, though there has been suggestions that the striker is holding out for Champions League football.
Sunderland have made a rapid and impressive start to the summer transfer window, with Simon Adingra, who is joining from Brighton, set to become the sixth signing of the summer.
But the Black Cats aren't finished there, and a keeper, centre-half and a forward remain priorities.
Suarez is one of several forwards said to be in Sunderland's thinking, as the Black Cats weigh up their attacking options. Armand Lauriente, Matthis Abline and Georges Mikautadze are other reported targets.
In goal, Sunderland are now ready to admit defeat in their pursuit of Djordje Petrovic, with the goalkeeper set to sign for Bournemouth.
Having already missed out on Marcin Bulka this summer, Sunderland will now take stock and assess their next move. Sam Johnstone is said to be one potential option, while Aaron Ramsdale has now been linked.