If JLR do want that land, and are willing to pay the footie club to relocate near the NEC, I am guessing it would be land off the NE corner of the M42 J6 (Bickenhill Interchange), opposite and North of the Motorcycle Museum. There is a large triangle of land there that is not Green Belt and is currently being used by HS2 (the M42, HS2 and the A45 make a triangle of land just there).
Curiously, the 'Interchange' station will be just there. That's supposed to be a 38 minute journey to Euston. Just saying.
Because of the M42, HS2 and the power lines that run over than land, it isn't Green Belt. It has sand pits, a Motorbike trail, all sorts of things.
Pretty sure that land has been snapped up for the huge ‘Arden Cross’ project. Homes, hospital, station, leisure spaces etc. could they fit a new stadium in there, maybe.