Novak Djokovic overcame injury issues and sweltering heat as he beat Jaume Munar to continue his bid for a fifth Shanghai Masters title.

The 24-time Grand Slam champion appeared to struggle with an ankle injury and called for the trainer on a number of occasions to receive treatment, but persevered to win 6-3, 5-7, 6-2.

On Sunday, Djokovic vomited during his win over Yannick Hanfmann in the previous round, which was played in temperatures of over 30°C and 80% humidity.

On Tuesday, Djokovic called for a medical timeout after breaking to go 3-1 up in the first set and grimaced as he received treatment to his left ankle.

After consolidating the break, he called for the trainer again before wrapping up the opener.

The Serb continued to struggle and grasp his ankle after points, but he managed to keep pace with Munar until the Spaniard struck the decisive blow at 5-4 to take the match to a decider, with Djokovic falling to the floor exhausted after a lengthy rally.

He was quickly attended to by the trainer and assisted to his chair before he had his blood pressure checked.

But, despite appearing devoid of energy, Djokovic returned to the court and broke Munar's serve at the first time of asking in the third set.

The world number five broke again to take a 5-2 lead before holding to wrap up victory in two hours 41 minutes.

Djokovic will face world number 44 Ziziou Bergs in the quarter-finals, after the Belgian came from behind to beat 31st seed Gabriel Diallo 3-6 7-5 7-6 (10-8) in the last 16.

Tenth seed Holger Rune progressed to the quarter-finals with a 6-4 6-7 (7-9) 6-3 win against Giovanni Mpetshi Perricard.

Afterwards, Rune called for the ATP Tour to introduce a heat rule similar to the one used at Grand Slams.

"It's brutal when you have over 80% of humidity day after day, particularly for the guys when they're playing during the day with the heat, with sun, it's even more brutal," he said.