The summer transfer window has now slammed shut for Premier League clubs but Arsenal could still sign a free agent. The Gunners made three additions in the window with Raheem Sterling making the switch from Stamford Bridge to the Emirates on deadline day. Though, one of their new signings Mikel Merino has already been sidelined through a shoulder injury, so perhaps they could dip into the free agent market for a replacement. With that said, there is a top-level midfielder available… READ MORE: Paul Merson shares what he really thinks of Arsenal signing Raheem SterlingArsenal could still sign A…