You couldn't really send him on loan anywhere outside the Premier League now, he's a full England international. He'd refuse any loan and have the PFA kick up a stink on his behalf. A transfer would seem like the best option. It is of course possible that he gets his head round how to be a team player at some point, he's still only 23; I don't know enough about Pochettino to know if he's the sort of manager who would be able to shape him. He's the sort of player that Wenger or Mourinho love to take on though.