Novak Djokovic will continue his quest to win a historic 25th Grand Slam title at the US Open on Sunday night. The Serb lifted his 24th Major trophy here two years ago, and has not won another of the sport's biggest trophies since.

The No. 7 seed will open his campaign against up-and-coming American star Learner Tien on Sunday night, but he's been warned that the teenager could cause him "a lot of trouble." Tien caused a huge upset at the Australian Open earlier this year, and he now has an extra boost, as tennis legend Michael Chang has joined his team and will be in his box for the match.

Chang made history at the 1989 French Open, becoming the youngest man to win a Grand Slam title at just 17 years and 109 days old. So he knows exactly what it's like to be a promising teenager on the tennis tour - and he believes Tien could give Djokovic a run for his money.

"I like his draw. Obviously Novak is one of the greatest players to play tennis, if not the GOAT himself. Learner has nothing to lose. He has everything to gain," Chang told the ATP ahead of their exciting first-round meeting.

"Certainly, growing up, Novak would have been one of the great champions he has watched growing up and he is the last of his group of unbelievable players: Rafa [Nadal] and Roger [Federer] and Andy [Murray], all part of that."

The former world No. 2 claims Djokovic would have won more Major trophies without Jannik Sinner and Carlos Alcaraz in his way. But he still wouldn't be surprised if Tien could pull off something special on Arthur Ashe Stadium.

The 19-year-old started the season ranked outside the world's top 100, but he qualified for the Australian Open and stunned Daniil Medvedev in the second round.

And Chang also knows the crowd will be on Tien's side when he faces Djokovic, as the world No. 50 is playing at home.

"I don't know how he's necessarily going to be coming out. We'll obviously expect him to play his best, as he always does, in Grand Slam events," the former French Open champion added.

"But Learner showed throughout this season that he can give the best players a lot of trouble. And he's beating some guys that had beaten Novak in past Grand Slams and he should draw confidence from that."

Djokovic will play his first match since losing to Sinner in the Wimbledon semi-final. The former world No. 1 skipped the Masters 1000 events in Canada and Cincinnati and later admitted he no longer had a proper schedule.

"I decided not to play because I wanted to spend more time with my family," he said ahead of the US Open. "And to be honest, you know, I think I earned my right and have the luxury of kind of choosing, picking and choosing where I want to go and what I want to play.

"I don't actually have any schedule other than Slams, to be honest. To be quite frank with you, I don't enjoy the two-week Masters events anymore. It's just way too long for me."

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