Go to kick-off and select the side with your Virtual Pro on it. Play against any side, it won't really matter. Go to "game settings" and adjust the "User Game Customisation". All stats should be on 50, so switch all of them that will benefit you (shot pace, pass pace, player acceleration etc.) to 100. Then go to "CPU Game Customisation" and do the same but adjust all the stats to 0. Play on legendary and put the time limit high so you've got a long time to unlock accomplishments for your player. You'll notice that the moment you start to play, it'll be easy to run by the computer players because they're so slow, and your players will be so quick. Very easy to boost your player.