Yes, unfortunately Neymar injury make his career not good at PSG. I heard in local media he will be available in September, but if you are saying is true he will be available in December that is very bad. Although maybe Al Hilal doesn't mind his injury but Al Hilal really needs the services of a striker at least to race for the title, it would be very disappointing if he only played half a season.
Neymar Jr is one of the most skilled player in the present age of football, his type is really rared. Unfortunately for the Brazilian, he have encounter critical challenges in his football career, which is injuries. The main reason behind his exits from Parc des Princes stadium this summer, the parisians started laying complaints about his inconsistencies in league games and severe injuries which greatly affected his performance negatively. However he moved to Saudi side, where he will gain regular playtime but he's currently injured and won't be available for games until he is healed.