Novak Djokovic is still setting "unbelievable" standards and remains the man to beat heading into the 2024 campaign, according to Holger Rune.
Twenty-four time grand slam winner Djokovic added another Australian Open, French Open and US Open crown to his collection this year.
The 36-year-old won a Tour-best seven singles titles in 2023 and finished top of the ATP Rankings for a record-extending eighth year in a row.
"I think it's great to see that Novak can still play at this level. It's unbelievable what he's doing," Rune said.
Only Carlos Alcaraz stopped Djokovic from landing a career first calendar Grand Slam with his triumph in the Wimbledon final.
However, if the next generation are to truly take the mantle from Djokovic, Rune accepts they need to start bloodying the Serbian's nose more regularly.
A challenge for the brave pic.twitter.com/t9V4FAnUkW— Novak Djokovic (@DjokerNole) December 15, 2023
Alcaraz was closest to Djokovic in 2023 with six tour titles, while Daniil Medvedev won five and Jannik Sinner four.
For all the talk of someone new potentially dominating the male game, though, Rune does not believe Djokovic's era of dominance is over yet.
"Alcaraz won a slam this year. Sinner finished in the top four. I was number four for the first time this year," he said.
"I think the next generation is very interesting. I think we are trying to compete with Novak and to see if we can match him.
"Still, he's winning three out of four grand slams - it's kind of tough. Before we can say that, we need to start winning more regularly against him."