The young defender is starring with Sporting CP this season and being tracked by the Gunners.
However, with a contract carrying a buyout clause of €80m, Sporting are confident keeping hold of the youngster.
Diomande only signed permanently for Sporting in January from FC Midtjylland - but he could've easily made the move to Arsenal at the same time.
Arsenal held talks with FCM, says O Jogo, but refused to pay the €10m the Danes were demanding for him before Christmas. The Ivory Coast international eventually joined Sporting for €7.5m.