When a player's unit value changes, how does that affect my current team?
Conversely, if your player does well and his stock rises, then this will means it will be more difficult for teams to sign him at the increased price.
If you drop a player for whatever reason, you may not be able to afford to buy them back later!
Also if you try to sign that player back immediately, you would have to pay the current price and not the original price you paid. Therefore please be cautious of this before selling players.