If they want to bring in European players to strengthen their defense, I think it will be quite difficult to get those who are still in their best form. Al Nassr may have enough funds to attract European professional players, but not all players will think about the money offer. Some who are still in their productive age will think about spending their best years in Europe.
Al Nassr must find another way to strengthen their defense.
Al Nassr have weakness in defense, but they will have to face with a bigger issue of the whole league. It's barrier for the league development in future seasons after three latest seasons with super star and star players from Europe and mass money spent. I read a report recently that appearances of Cristiano Ronaldo, Karim Benzema, Mane, Neymar, Brozovic, and more star players from Europe latest years, are not enough to increase total spectators in each match in Saudi Professional League.
The Saudi Professional League and investment from PIF and attention from Saudi Arabia government will have to reconsider their developmental strategy for the league, and their national team. So far, spending mass money seems to not work too well as expected, it's kind of buring money quickly while impacts on young players and national team are not too good and uncertain in future.