World number one Novak Djokovic reached his 10th French Open semi-final but suffered an injury scare before beating Spain's Pablo Carreno Busta 4-6 6-2 6-3 6-4 on Wednesday.

A month after being defaulted for inadvertently striking a line judge with a ball while playing Carreno Busta in the U.S. Open fourth round, the 33-year-old Serbian found himself in trouble once again.

This time it was nothing more sinister than apparent physical problems with the top seed wearing tape on the back of his neck and his upper arm requiring treatment.

Carreno Busta, who lost in the U.S. Open semi-final after leading German Alexander Zverev by two sets, took advantage to win the opening set – the first conceded by Djokovic in the tournament.

Djokovic looked flat and had to save break points early in the second set before raising his game at the important moment to win the next two sets.

Carreno Busta hung on gamely but Djokovic was superior when it mattered and one break in the fourth was enough to set up a last-four clash with Greek Stefanos Tsitsipas, the Serb's 38th Grand Slam semi-final.

Djokovic's dramatic demise in New York deprived him of a chance to win an 18th Grand Slam title and move to within one of Rafa Nadal's haul and two shy of Roger Federer's record.

He looked relieved after avoiding another setback against the Spaniard he has found such an awkward customer of late.

"I started this match a bit badly with bad movement. After I found rhythm and confidence," Djokovic said afterwards on Court Philippe Chatrier on another damp and chilly night.

"It was important to stay focused. Many players have said it before me: these four Grand Slams matter the most in tennis history.”

"I had some neck and shoulder issues. I'm still in the tournament, so I don't want to reveal too much. I'm feeling OK. As the match progressed, I warmed up and the pain faded away. It allowed me to play better and feel better."

In response, however, Carreño Busta said: "That's normal, no? He makes always [such gestures]," he said. "The last years he's always doing this when he has problems on court. I don't know, maybe it's the pressure or something that he needs to do it. But he continues playing normal, no? I don't know if he's in pain really, or he has mental [issues]."

(With input from Reuters)