You won't get more, it's just a waste of money to sell him without running his contract out. His 8 games are worth something, depending on how much he is worth. Perhaps one million of more. If you don't play him, it's like throwing that money out the window. What you get for him when you sell him is not going to change much, but the only bad move you can make is to not run out his contract. If you don't, then you have to pay another player to play those games. There's no getting away from it.
Make sense?
Perhaps what you're missing is the fact that when you buy a player for, say, 5,000,000 you are paying his transfer fee plus his contract for ten games. So, his real value (when you sell him) is just the transfer fee, so something like 4,000,000 if his contract costed 1,000,000. You get the 4 million back when you sell him, but you never get the contract back. You only get value for it by playing him in matches, and like I said, that's real value because no matter what you do you have to pay SOMEONE to play those matches.
One alternative would be to buy a really cheap player who you prefer and play them instead, but they would need to be a lot cheaper, and this would only maybe cut your losses slightly, but still it would be a loss.
They key then, as you can see, is to be very careful with who you purchase!