One of the players I follow on milb.com has been told to report to the Arizona Fall League. My understanding is the AFL is for prospects projected to ultimately make the MLB roster.
The player in mind signed for significant money. But he was passed at his position by a younger prospect who has had his position changed after moving up past him. The reason is there's no way in hell anyone is going to play their specific position on the MLB team (stuck behind an all star).
It would make sense to change this player's position to the one possible place he could eventually compete for a major league roster spot. But even then he would be stuck behind two or three more highly regarded players. The one position is the only conceivable position opening in the next two years he could win at the MLB level.
The MLB organization could lose this player in the Rule 5 draft in two years. While he has potential his organization is loaded with prospects making it difficult to be placed on the forty man roster.
Would a prospect be sent to fall instructional for showcasing for a possible trade? His stock is at it's highest point based on this season. The reason I ask is any organization loaded with prospects is prime for trading a package of them for an established player.
If my explanation seems a little vague I'm trying not to identify the player.