Yes, injury is an endless nightmare that Neymar feels, almost every time he is constantly injured, even though it is not a serious injury that requires him to be sidelined for a long time, even a minor injury will keep him out and unable to play.
It is like his destiny and a joke of destiny against him. He always got serious injuries when Champions League or World Cup comes to important matches. He is responsible for it with overwhelming entertain time in summer and Christmas, New Year vacations. However it is joke as he did not miss unimportant matches instead of very important ones. I can't say it is because of destiny or only coincidence.
Yes, sometimes things like this become a factor where the player has to decline, even though if you look at his actual appearance he is still very good. The decline in Neymar's market value proves that it really has a big impact on his appearance. At a time like that, other clubs will also consider signing him more, because they will also think about why bring in players who sit a lot on the bench to rest.
Injury is part of reasons but his age contributes to his estimated transfer value drop too. Clubs have to think so carefully if they have to spend transfer cost which is not cheap and give Neymar high salary. They buy a player and hire him to help them win titles but Neymar with his past injuries actually brings some fear to rich clubs.
You're right, I just realized he is a player who often gets injured in important matches. The bad luck he had with injuries which always happened when he was going to play important matches, especially during the World Cup in Qatar for example.
I'm sure no player wants to get injured, but it can also be because of bad habits. Even at the age of 40 they can still play even if the speed is reduced due to age. From what I see Ronaldo might be a good example of keeping fit, while other players his age are starting to lose control of their body development, he can still be as we can see.
Neymar is a player we often hear about getting injured at a very mature age for a footballer, and slowly indeed it could destroy his career and affect the club's interest in him.