The management of Sporting CP is not honoring the agreements that he had with them, and that is something that he, as a player, is not happy about. The fact that he is unhappy with the club makes his move away from the club more imminent because, from what I heard, he has refused to train with them. I think in the coming days we will hear positive news about him moving to Arsenal because so far we are the club that he has been linked most with to join.
Arsenal are starting to shift their focus to other players even though they previously said they were quite interested in Gyokeres. This is because Sporting are asking a price that is high enough that Arsenal cannot afford to recruit him and if this condition continues then Gyokeres' future is increasingly unclear. If in the end the transfer fails and no other club is interested enough to recruit him then whether he wants it or not he will stay and it may be true that Sporting are not respecting the agreement they have made with the player because they are reluctant to let him go for the price that Arsenal is asking.