From what it looks like, the black shorts and black socks are part of an away kit. Bradley is in the middle of some kind of opening training session, as per the location of the shoot. That, or he is there to do the promo shots for the new away shirt as well as taking a player profile shot. Based on the angle of the lights, it is possible that a white board is behind Bradley, hidden from sight. It is placed further back so as to prevent shadowing with that direct light.
Now, because all players wear home shirts for profile pictures, they quickly swapped the black-and-red away shirt for a profile shot, but didn't bother with the shorts and socks since the photo is usually mid-chest up, and hung the away shirt away from the shot, perhaps on one of the light posts.
Then, this behind-the-scenes shot didn't get the full away shirt out of the way, and what we're left with are strange shorts, socks and a black sleeve with red trim.
https://i.imgflip.com/64m5w.jpg