Wow, that's not good news at all, especially since Winnie himself said his lack of game time was more due to a) the Hammers' relegation battle and b) his lacking the 'rhythm' of training and playing at that level.
I guess Nashville were probably going to pay a good chunk of his salary so they did their due diligence and put him through his paces and gave him a thorough medical
EDIT: Found this tweet from MLS correspondent Tom Bogert. No mention of a failed medical but hard to think why else they would pass on him at this stage