Novak Djokovic has addressed an injury scare he suffered during his three-set comeback win at the Shanghai Masters on Friday.

The world No. 4 stormed back to beat teenager Jakub Mensik 6-7(4) 6-1 6-3. But he felt some discomfort as the match went on and started to grab his left leg, stretching it out.

Djokovic is now hoping he will be ready to face Taylor Fritz in Saturday’s semi-final.

Djokovic has already faced issues with his right leg this season. He hurt his knee at the French Open and underwent meniscus surgery soon after. Since his return, the 37-year-old has worn a knee brace while competing.

But it was his left leg that posed a problem as he came back to beat Mensik in the quarter-finals. While serving at 3-2 in the final set, Djokovic had to turn away.

He bent over in pain before attempting to stretch the muscle out, also leaning over to grab it. In the next game, with Mensik serving, Djokovic barely went for the returns and conserved his energy for the end of the set.

The fourth seed eventually got the job done and addressed his knee troubles after the match, though he seemed to have no concrete answers about the problem.

"Yeah, I mean, it's a strange feeling, to be honest, those couple of points in that game, but after that it was fine," he said of the moment he had to stop and stretch out.

"So, hopefully when it cools down I'm not going to have any troubles with it, because I already have troubles with the right knee, so it wouldn't be great. Yeah, let's see what tomorrow brings."

It's no surprise Djokovic was feeling it in the final set as he was made to work to beat the world No. 65. After serving for the first set, the Serb was broken back and dragged into a tiebreak.

He raced into a 3-0 lead before some sloppy mistakes started to slip in and Djokovic only won one more point before Mensik took the opener 7-6(4). But he came back to reach his sixth semi-final of the season.

Afterwards, the four-time former champion said: "We went toe-to-toe until the last moment, until the last game. I was fortunate to really find great serves in the last game, a couple of aces, that helps. I didn’t serve that well end of the first set when I was serving for the set at 5-4.

"Managed to turn things around. I played quite a bad tiebreak, you know. Just kind of stayed collected, started off very well in the second set. I felt that we both had a little bit of a physical crisis beginning of the second. I think we pushed each other a lot. A lot of long rallies. Tough battle, almost two-and-a-half hours."