The 25-year-old is travelling to Turkey today to sign a permanent deal with the top-flight side.
It is understood a low six-figure transfer fee has been agreed between the clubs.
Mallan enjoyed his time on loan at YMS last campaign, scoring twice in 17 games.
He returned to Hibs in the summer but admitted he was keeping his options open.
The midfielder featured in friendlies against Dunfermline Athletic and Stoke City but wasn't in the squad for the Arsenal game on Tuesday.
Turkey is an attractive proposition for players and Mallan revealed in June how much he enjoyed it.
“Rarely does this kind of opportunity arise so I felt it was something I had to do,” he said.
“I wanted to challenge myself and I played a lot of games and came up against teams like Fenerbahce, Galatasaray and Besiktas, top class teams like that. So, I am glad I went."