Novak Djokovic has been the best player this year, winning three of the four Grand Slams this year. He's number one on the ATP Tour right now and has a pretty decent shot of finishing the year as world number one as well.
The player who could disrupt all of that is Carlos Alcaraz, though he'll need a special finish to the year. The Spaniard has been quite spectacular this year, winning Wimbledon by beating Djokovic and positioning himself as his biggest threat.
Ivanisevic would agree with that as he sees Alcaraz as the true rival of Djokovic, the player closest to beating him.
It will stay that way (Alcaraz being top of Djokovic’s list of rivals). There are other good tennis players, especially Daniil Medvedev, and Novak’s big opponent could be the Italian Jannik Sinner, who also knows how to get into a crisis, but it seems that he absolutely does not suit Alcaraz, and Novak could also have problems with him.
Although it is actually too difficult a word and as long as the relations in men’s tennis are like this, it is difficult to see someone who could compete with Djokovic for a position in the world rankings for a long time.
Djokovic certainly still looks like the best among the best, which speaks more than enough about the legendary tale of the Serbian. Alcaraz is a challenger, but he's not yet eclipsed the master. There are other challengers as well, but they, too, haven't managed it yet.
Will they be in the future? It's likely, but for the time being, it does seem like Djokovic still leads. We'll see what happens in the coming weeks with the Paris Masters and the ATP Finals right around the corner.