Arsenal target Viktor Gyokeres is facing disciplinary action by his club Sporting after failing to report for pre-season training, says the Portuguese club's president Frederico Varandas.
Varandas added that any potential transfer was now becoming "more complicated".
BBC Sport reported last week that Arsenal sporting director Andrea Berta held face-to-face talks with Sweden international Gyokeres in Portugal.
Sources have told BBC Sport that talks are ongoing with Arsenal, who are still hopeful of striking a deal, with their most recent proposal for the 27-year-old totalling about 70m euros (£60m) including add-ons.
Last month Sporting president Varandas said there was no 'gentleman's agreement' for Gyokeres to leave for 70m euros but added that the club would not demand his full release clause of 100m euros (£85m).