World number one Novak Djokovic admitted he was "worried" about his French Open title defence after falling to 44th-ranked Czech Tomas Machac in the Geneva semi-finals on Friday.

Djokovic went down to a 6-4, 0-6, 6-1 loss having taken a late wildcard into the Swiss clay-court tournament in a bid to reverse an alarming dip in form ahead of Roland Garros where the 24-time Grand Slam champion has won three times.

"Of course I'm worried. I haven't been playing good at all this year," said 37-year-old Djokovic.

"I've had some good matches here and there but it is what it is. You have to accept it. I don't consider myself a favourite there. I'm going to take it match by match and see how far I can go."

The Serb will head to Roland Garros where he faces Frenchman Pierre-Hugues Herbert in the first round having won no titles this year, his first such dry spell since 2018.

Djokovic, bidding to reach his first final of the season, received a medical timeout at the end of the first set and revealed he had been suffering a stomach complaint.

"It was a terrible feeling with stomach and health today -- it was not a great night and today as well," said Djokovic to atptour.com.

"But I don't want to take anything away from his win, he deserved it. I don't know what to think about this match to be honest. I want to forget about it and move on to Paris."

While in Geneva, Djokovic became only the third man after Jimmy Connors and Roger Federer to rack up 1,100 tour wins.

However, even that will not ease the worrying fact that Djokovic is just 14-6 this year with runs to the semi-finals at the Australian Open and Monte Carlo Masters his best performances.

"It was good that I could come here and play more than one match. I played three," added Djokovic.

"I just need to feel better. It's not enjoyment when you are suffering on the court feeling this way. You're not able to focus on tennis when you have other stuff happening. I just hope I can be fit and ready and prepared for Roland Garros."

Djokovic, bidding for his fourth French Open title, could lose his number one ranking in Paris to Jannik Sinner and must reach the semi-finals to have any chance of keeping the Italian at bay.

Machac, competing in his maiden tour-level semi-final, rallied from a break down in the first set on Friday and after failing to win a game in the second powered back in the third set.

"I'm looking forward to playing in a final for the first time," said Machac who will face two-time champion Casper Ruud or Italian Flavio Cobolli in the title match on Saturday.

Their semi-final was suspended later Friday due to rain.

On his win over Djokovic, the 23-year-old added: "I have no reaction right now, I just fought for every ball.

"When you play against Novak you just hope. You just try to play your best and see what it looks like."

Ruud, the world number seven, was the runner-up in the last two French Open finals, including a defeat to Djokovic last year.