After the world cup, there may be differences in appearance for some of the top teams in Serie A, especially for teams whose players are used in world cup matches. Of course they will be very overwhelmed and tired, even potentially injured. But in general Napoli will still try to perform well after the world cup because not many of their players have been involved or called up by the national team in this world cup.
World Cup have two impact side for team, positive side with their player have on the high physical quality because one months keep in training center with their national team, but have negative impact for team when their player return back later with injured. I think have different appearance with top team standing in Serie A later based on how many main player get injured after World Cup. Lately have one player confirmed with injury is Neymar, just waiting few matches later who become next player get injured and give bad thing for their current team.
Napoli in the top standing right now need controlling their player without any serious injured when returning back to the team, I think if not any player injured nothing difference standing position in Serie A and Napoli can continues consistency performance.
Injuries will be a threat to players who appeared in the World Cup when they return to the club. And that will have an impact on the club itself because they have to lose their injured player. Napoli sent 5 players called by their country to participate in the World Cup. I think their percentage will be less, and it will reduce their risk of losing a lot of players to injury when the World Cup ends. I also think that for Serie A Napoli will be able to maintain the performance like before this World Cup break.