Usually the time of the season when there are more games in clubs is between December and January. This means that national team players will go to their clubs after the World Cup and may be more tired than usual. We can't forget that the world championship has a lot of games in a few days, which can become complicated even in the middle of the season.
all the other will have a time to rest in the middle of the season, Calcio would not be that affected IMO, since Italy is watching World Cup from home
nevertheless, that could bring up some smaller teams, that do not have international stars into top rows, and make season more interesting in the end, since Top teams will have tired players, and need time to play-up after the World cup
There are going to be a few problematic situations. We all know that a lot of players really favor playing club football instead of international football. So, it is going to be a little tough to make younger players play in the world cup and also make the players happy.
They are obviously good players but the problem is everyone has a different mindset and someone can think differently compared to others and he cannot be punished for that. But in the end club football is never going to be able to bring the glory that comes with winning the world cup