That risk is the same for almost all teams because there are all those tournaments that inevitable bring a lot of games. Whether it is Conference League. Europa League or the CL, everyone has at least those games from the group stage or league stage and then the round of 16 games. The only problem I see is if teams get unlucky and have several injuries without impact from their opponent players. That would be a sign of fatigue, but if they get injured because of attacks in game, there isn't much you can do about it.
That's why squad depth is quite important because the coach can make a number of rotations at certain times of the game. Almost all teams will experience conditions like this but how a coach can see the opportunities to solve them. Almost all teams that play in the Champions League participate in a number of other tournaments as you said and injuries to several key players can cause quite a big problem. Like what happened to Real Madrid in the previous season and they failed to achieve the best results in winning the title because they were affected by injuries to several key players.
That is why great players have to have both, the skills and ambition to play their best, but simultaneously the biggest talent is going to fail if they are extremely prone to injuries. Coaches are lucky and happy when they have those top players that can play 50 games without any muscle issues or other problems. Rotation is not always the solution, I think it's a lot about genetics of a player and how medical treatment and recovery is done. I know that rotation can and should be part of those routines, but it still depends on the player. Some players go 50 games and more per season and never get injured, some players can't play half that number and are constantly fighting injuries of all kinds.
Replacing superstars is usually impossible, but squad depth is important if the best teams want to compete for as long as possible in all competitions. If it is not possible to replace a player 1:1, you still want highest quality in the squad. But it is a balancing act as no great player accepts their role on the bench while normally no great player ever wants to leave the game early. Someone like Haaland or Mbappe would never accept if they had to leave the games after 60 minutes every game.