There's two questions here: Who is the player and what are we sending in return?
The first name that comes to mind is Tim Parker of Vancouver. That being said Goff is reporting of trade talks between Red Bulls and Vancouver for Parker.
So who does that leave? Hedges, Opara, Parkhurst, Marshall, Besler, Moor, Birnbaum.
Too old or too highly valued by their current team.
Maybe Maund of Vancouver or Glaad of RSL. Also floating Christian Dean of Chicago. Miles Robinson of Atlanta would be a name out of left field.
In return for a backup, young American CB for this team? McNamara would be too much. Maybe some GAM/TAM but we need to trade for international roster spots even if Chanot and Villa get their green cards with Ofori coming in, hopefully.