#4 Mesut Ozil
Along with Sanchez, Mesut Ozil's Arsenal stint comes to an end in June 2018 unless Wenger and Arsenal sort out his contract issues. Wenger, while recently stating that the Chilean is going nowhere, also mentioned the German playmaker as another key player who will not be sold.
While the club tries hard to keep two of their best players at the club, Ozil has claimed in the past that a move to Turkey would interest him the most once his time with Arsenal is done. A creative genius on the field, Ozil is unlike any player in the league and can split open defenses with a single pass.
A vital component of Arsenals attacking play, Ozil's departure could hurt the Gunners, maybe more than the Chilean departure. However, the German WC winner looks set to stay with the club. However, his contract must be taken care of quickly by the club, or they Arsenal will risk losing another top quality player on a free transfer before the start of next season.