Europe and the US are still closed off to each other?
The MLS crew might be useful for this fixture.
A solely Europe based run on side could be something like -
Woud, Cacace?, Pijnaker, Smith, Themi, Dalton Wilkins, Bell, Thomas, Singh, Just, Wood
Could be a little ugly without any of Reid, M Boxall or Tuiloma.
Old? Probably played the most minutes of any kiwi in a half decent professional environment over the last couple of years.
If game goes ahead and is restricted to solely Euro based players, then yipe 34 yr old Steven Old would be in the mix. But don't forget he was playing for a bottom club in League Two, a team ranked about a lowly 90 on the English Pyramid.
Really there would be nil future value in having guys like Old or Themi (also 34) playing, but if you have to cobble a squad solely from Europe together, they would probably both be in there.
I imagine one of the many factors to get sorted, before confirming the game, is whether travel between the US and Europe will open up without any quarantine requirements at either end. With fears of a '2nd Covid wave', doesn't seem Americans (or those resident in the US) will be welcomed to the old continent any time soon.
If the MLS guys could travel freely to Belgium with no quarantine requirements, Hay could assemble a pretty strong side (injuries permitting).
However remaining MLS regular season dates post the current Orlando tourney (finishes early August) have still to be confirmed. MLS season normally finishes November, with those teams not making the playoffs all done by October. However this MLS regular season may go longer into November - playoffs December even (though by then the winter snow/chill can be happening in northern states!).
In other words many of the US contingent may not to available for an AWs v Belgium game scheduled for 8th October, even if travel between US & Europe has opened up.
An AWs side without it's US based defenders, would be a far weaker side when forced to roll out the likes of Old, Themi or any greenhorns like Pijnaker, Wilkins etc. Also Smith hasn't played for months, and is currently sans a club.
Good news (or bad news on your point of view), is that if the game goes ahead it will likely be Belgium 'B'. The Belgians have a UEFA Nations League, scheduled against England (Wembley) a few days later on 11th October. That will obviously be the first choice Belgium side, who are also scheduled to play Nations Leagues games in September (Denmark & Iceland). If those Sept games go ahead their top players won't need an extra match against lowly NZ.
So like the Irish game last November, expect the hosts to roll out a 2nd string side.