Regarding the world cup and the club that a particular player participates, there may be some kind of clash of interests, as there may be several unpleasant events during a world cup, injuries, unavailable that a player may suffer when he returns to play at your club or even the attrition/fatigue that a player may experience after participating in a world cup.
If I'm not mistaken, according to FIFA rules, a club cannot refuse a player to participate in official matches by countries. Therefore, even with conflicts of interest, it is a risk that everyone will have to accept.
What happens sometimes is that the club and player make some persosion with the technical team, to be little used on certain occasions.
1. The Match Only Runs 2x30 minutes
2. Stop Time When The Ball Comes Out Or There Is A Violation
3. There Are No Throw-ins
4. No substitution limit for player
5. Players who get a yellow card can be suspended for 5 minutes
so it's possible that if a player gets injured and can't play then the management or coach may include him to sit on the field on the bench but to go into the match directly in my opinion it's very risky because it can accidentally worsen the injury of players who force themselves to play when his condition is still not fully recovered.
In fact, the World Cup is more of an entertainment for ordinary people who are not usually interested in football. True fans understand that the most important thing happens at the club level because there is a more flexible system than "I was born there and can only play for one team in my life." 
