SHANGHAI, China (AFP) — Novak Djokovic said he was “concerned” about his physical state, but still dispatched Belgium’s Zizou Bergs 6-3, 7-5 to set up a Shanghai Masters semi-final against tournament surprise package Valentin Vacherot.

The 38-year-old Serbian, the highest-ranking player left standing, is getting ever closer to a fifth title in the Chinese financial hub despite struggling throughout the week.

Next in the crosshairs of the 24-time Grand Slam champion is world No. 204 Vacherot, a qualifier from Monaco who battled back from a set down to stun Holger Rune 2-6, 7-6 (7/4), 6-4.

“I’m concerned, too,” Djokovic said when told his fans were worried about his health, adding there were “issues that I’m trying to address day by day.”

“I don’t want to talk about the details. I’m still in the tournament. So I prefer just focusing on recovery and trying to give it all.”

Djokovic broke in the sixth game after an unforced error from the 44th-ranked Bergs.

But just days after he overcame exhaustion, vomiting and an injury scare in his last match against Spain’s Jaume Munar, he looked tired and overheated.

“There’s always something happening with the body, pretty much every match that I play right now,” Djokovic said wryly.

He took a puff from an inhaler during a break in play as his team anxiously looked on, but took the first set.

Djokovic broke for a 5-4 lead in the second set, but Bergs broke back after a series of thrilling rallies that drew screams from the crowd.

The umpire had to ask the spectators for quiet multiple times as fans chanted furiously for Djokovic, waving Serbian flags and signs reading “Novak is the GOAT” (greatest of all time).

When Djokovic broke again for a 6-5 lead, the stadium erupted.

Bergs still would not lie down, saving two match points and creating another break point of his own, but Djokovic finally got over the line when the Belgian went long.

“I’ve been struggling quite a bit with energy levels, and just every opportunity that I get, the crowd feels it... I can hear that noise and that energy drives me,” Djokovic said.

Vacherot, the lowest-ranked player to make the quarterfinals, said it would be “unreal” to face Djokovic.

In stark contrast to the Serbian, the 26-year-old said: “What I’m really happy about is my fitness... My body feels amazing.”

When he landed in Shanghai, Vacherot was still on the alternate list for the tournament — meaning he wasn’t sure he would even get the chance to play in the qualifying rounds.

World No. 11 Rune broke in the third and seventh games to win the first set comfortably.

Watched on by his cousin Arthur Rinderknech, who will play in the quarterfinals on Friday, Vacherot took a tense tiebreak in the second.

Rune looked increasingly rattled and frustration came to a head in the seventh game of the third set when he received a time violation and committed three unforced errors to hand Vacherot a break.

Vacherot served out to secure an unlikely victory, falling to his knees in disbelief.