Jhon Duran was given temporary leave at Zenit for personal issues. Since moving to Al Nassr (and doing quite well to start with) he's ended up having a long series of absences, being loaned out a couple times and not playing at either Fenerbahce or Zenit (despite playing well when he is on the field, rarely).
A lot of drama surrounding him, and also when he was at Aston Villa, but it seems the causes are more multi factorial than him just being a clown and having a bad attitude. He was accused at Aston Villa of being a bit of a clown and Mourinho said he has a bad attitude.
In October Fener's new manager said that Duran had been playing with pain for a long time, for several years, and playing through pain at his past clubs. The reason he didn't play him is because, according to him, the pain barrier had become too difficult for Duran to continue playing through.
Then they said that he had osteoarthritis and he took 2 months out undergoing some treatments before returning to play some minutes, but still not much, then going on loan to Zenit, where he hasn't played very much and is now taking a leave of absence.
All of this looks like a bit of a mess, a player with some commitment/attitude issues along with long standing possible joint issues and it feels like he might fall out of football.
However, he's only 22, he's still really young and has plenty of time to put the issues behind him. Further scrutiny of his health record would be needed but if its something that can be managed/healed over time he could get back to a high level in the future. He probably would benefit from some patience and maybe his attitude issues are a reflection of a difficult situation.
I think we should investigate his case in case he would become free. Who knows how the situation will go but if he becomes a burden for Al-Nassr they might just let him leave and spend big on someone new. Of course, we'd have to thoroughly check and make sure there are no major issues, that will be up to the medical team, however if its not career ending we could consider bringing him in and slowly rehabilitating him.