This is a situation where contracts of players and managers gets a bit hairy. On the one hand, you have the rights of the players to move between clubs freely - the free movement of labor being a protected legal right. On the other hand, I would not be surprised if certain managers had clauses written into their employment contracts that say something to the effect of "I will not sign Player X from my old club within 1 year unless..." We don't really know for sure what the terms of the contract are, but it could really go either way.
On one hand the modern day athletes demand guaranteed contract. The club is obligated to pay their full wages even if they massively under performed. You can't just get fired with 2 weeks notice like an average Joe.
On the other hand they dare to fancy the freedom of movement between clubs at anytime, under said guaranteed contract.
That logic just does not seem right to me.
I heard arguments that a club doesn't have to sell when faced a transfer request, but in reality not many clubs can afford a high wage bill sulking and possibly affecting team morale, and watch the transfer value dwindling to zero as his contract approaches expiration.