"He has turned up in fantastic shape," said coach Danny Hay. "Whilst he hasn't been playing regularly for some time now, injured and now unattached in terms of his club life, he has clearly been looking after himself, training hard and I would go so far as to say he is probably in the best shape of his life."
Reid's career has been cruelled by injuries in recent years.
He started the 2017-18 season as a first-choice centre back at the Hammers and was even captain in eight games between September and early January.
But he suffered a severe knee injury against Swansea on March 3, 2018, which ruled him out for the best part of 18 months, and by then there was no going back, in such a competitive Premier League environment.
But Reid wants to make the most of the twilight of his career, both with the All Whites and at club level, as he hopes to secure a new home in the January transfer window.
Hay said the ultimate decision on Wednesday's game would be left up to Reid, but the signs were promising.
"Initially we wanted to protect him, knowing that he hadn't been training in a proper football environment, ensuring that we didn't put him under pressure to play," said Hay.
"But he has come in looking great and feeling great so it's exciting. Hopefully we will get some minutes out of him. If he feels like he can contribute in a positive way on the pitch, then I will certainly want to encourage that."
After using an experimental line up in the 2-1 win over Algeria 'A' on Saturday, Hay will revert to his top XI on Wednesday. Sarpreet Singh is also likely to be in the frame, having made good progress after coming into camp with a minor knee strain.
Gambia will be a difficult test. Their world ranking of 147 is probably misleading, more reflecting the strong levels of competition across Africa.
They have had wins over Gabon (88), Niger (121), Angola (129) Togo (134) over the last 12 months. Gambia boast a strong squad, including highly rated Bologna striker Musa Barrow and Sampdoria centre back Omar Colley.
They are among several players based in Serie A, with the rest of the team drawn from top European leagues, and Hay expects a tougher test than the All Whites faced against Curacao and Bahrain last month.
"Gambia [have] players at a good level in Europe," said Hay. "They are athletic, quick, very powerful and that is something a little bit different, that we haven't faced.
"This is a bit of a journey for us. We had a two-year hiatus, during which time players started to cement themselves in their clubs around the world but ultimately it is nice to be able to have the players back together playing regularly."