Raising market value

Is market value a fixed number for each player or can it increase/decrease depending on whether or not you are training the player?

I'm trying to decide whether or not to waste my efforts power training a high valued young player whose quality is below average on my team. He's a fast trainer (approx +200 in match), but it could take time getting him to reach my team level. Trying to decide whether to just sell him and use that money to buy a higher quality player.

I rather not.

Buy always 18-19yo 5* player which is close to get sixth star (ex. 53,54), then he can be about 3 or even 4 seasons in your team with 5*.
The more the player cost the more quickly he will develope.

So his market value wouldn't go up even with some power training?

As they increase the value increases. I had 300k added on to total value after two games earlier.

Okay, thank you both for the responses :)