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The north London club will reportedly pay £14 million for the Portuguese midfielder, with Harry Redknapp hoping to add more depth to his squad in a bid to push for the Premier League title next season.
According to the Turkish media, representatives of the two clubs have already shaken hands on a deal that will go through during the summer transfer window.
Fernandes has been a regular for the Black Eagles this campaign, contributing towards his side's current fourth place position with three goals.
The Portugal international has previously enjoyed loan spells in the Premier League with Everton and Portsmouth.