The midfielder will be Arsenal's third most expensive signing.
Arsenal have agreed a deal for the midfielder, and the player has already completed his medical ahead of the move.
The player was pictured in an Arsenal strip last week, and it transpires that they rushed forward to allow him to link up with Switzerland ahead of Euro 2016.
The Borussia Monchengladbach midfielder flew into London on Friday to complete the process, and that is when the pictures were taken.
He is now set to finalise the deal, with the Mirror reporting that Arsenal hope to have the move done in the next 48 hours.
It is believed Arsene Wenger was keen to rush through the transfer in an effort to try and lift the mood around the Emirates following a disappointing campaign.
The midfielder will be their first signing of the summer transfer window, and at £30million will become their third most expensive signing behind Mesut Ozil and Alexis Sanchez.
Gunners fans will be hoping he is one of several arrivals at the club, with them also keen to see a world class striker arrive at the club.