If modric is in a team that has players willing to play, he also is going to be willing to play. Modric in a team that has Ronaldo and all the players that Al-Nassr FC has will make Modric to be willing to play because he'll be getting the motivation to win trophies. Ronaldo changed the mentality of the Al nassr players but Benzema thinks he came for vacation and he's only enjoying himself while the team is doing all the work, this is why he has being playing badly. Ronaldo teams has Sadio mane and others always trying to win every single game therefore modric should be very selective of the teams that he'll be going to join or he'll end up becoming a bad footballer as Benzema is becoming. Saudi leagues isn't competitive to the standard of trying to be a solo player, you need everyone in the team to have an impact on matches and winning them.
Modric has already answered a hundred times about moving to Al-Nasr, he says that he really hopes to stay in Real Madrid, but the contract has not yet been signed. Perhaps there is nothing wrong with this, if a player feels that he is in good shape and can continue to play at a high level, then why should he not continue to play for his team. In any case, if his performance deteriorates, Ancelotti can always replace him.
There is also the problem that with age the likelihood of injury increases, remember how many injuries Ibrahimovic had when he continued to play in recent years. But Modric always seemed to be doing well, I don’t remember him spending much time with any kind of injury.