Dominic Thiem says Stefanos Tsitsipas won't be waiting around to make a major mark.

The Roland Garros runner-up says the NextGen label thrust on Milan champion Tsitsipas and finalist Alex de Minaur is a bit misleading.

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Thiem believes both Tsitsipas and de Minaur are already true contenders.

"I'm not really considering Tsitsipas and De Minaur as Next Gen," Thiem told the media in London after winning his final ATP Finals match. "[Tsitsipas] is No. 15 in the world, played finals of a Masters 1000. He's completely established in the absolute world class. De Minaur the same, he will also be top 20, top 15 next year."

At Roland Garros in May, Thiem topped Tsitsipas, 6-2, 2-6, 6-4, 6-4, avenging a straight-sets loss to the Greek in Barcelona. Thiem believes the leading youth on the ATP Tour are more advanced than he was at the same age.

"It's just amazing and also interesting to me when I came up, I was first time top 100 with 20 and a half," Thiem said.  "I was the youngest there basically. Now they're way younger players in the top 100, way further already. I think it's changing a little bit again. Way younger players are having their breakthrough earlier again than it was four or five years ago when I did it."

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