This idea is way off the mark. Game conditions and practice conditions are almost entirely different. Any who have played the game competitively know this to be true.
Certainly a player can improve their skill level by practice, that is a given. BUT, team practice is MOSTLY made up of drills. These drills are mostly individualistic. You will also find a fair amount of conceptional thinking (strategy), and theory (this is what we want to do) in practice.
Games comprise NO DRILLS, and no theory. Game conditions are fast, competitive, and fluid. Team performance is the focus. In-game, players are in situations where they are required to react quickly, and make solid, nearly instantaneous decisions. In games, players are testing themselves against competition that is trying to defeat them.
I could go on with the analysis (comparison) between game and practice, but I won't, the point is made. Totally opposite conditions.
If you want a player to get better re: game performance, then you have to expose them to significant game conditions.