World number one Novak Djokovic suffered a shock defeat to Japan's Kei Nishikori in the Basel semi-finals.

The Serbian player lost 2-6 7-6 (7-4) 6-0 in Switzerland as he went down to only his fourth defeat of the season.

The tournament was the first Djokovic had played after six weeks out with a back injury and he is unsure if he will be fit to play the Paris Masters next week.

"I don't think I'll be able to train for the next few days," said the 24-year-old. "But I think I'll go straight to Paris."

For Nishikori, the victory follows his semi-final appearance at the Shanghai Masters last month.

"It's unbelievable," said Nishikori. "In the second set I started playing well and getting a rhythm."

The 21-year-old will face either Roger Federer or Stanislas Wawrinka in the Basel final on Sunday.