It's a strange world, that of football.
Regardless of how useful a player could be to a team, no matter how desperately they need a new striker or a new goalkeeper, fans would refuse to see certain players lining up for their club.
For some it's association with a long-standing rival, for others it's a controversial past.
In other instances, the player may not sign for a club because of his advanced years.
Here we take a look at five signings that really should happen but, for one reason or another, almost certainly won't.