This is concerning ...
Steelers star JuJu Smith-Schuster posted video appearing to show him in the driver's seat of a BMW, hitting 104 MPH ... less than 2 weeks after suffering a severe head injury.
The Pittsburgh WR posted the video on to his Instagram stories late Tuesday night ... seemingly wanting to show off his fancy ride and the Travis Scott banger that was playing over his car's speakers.
The problem for JuJu? He suffered a serious concussion in the Steelers' game against the Browns on Nov.