Jiri Lehecka progressed to the first ATP Masters 1000 semi-final of his career as Daniil Medvedev retired hurt on Thursday at the Madrid Open.

Lehecka, who beat the great Rafael Nadal in the last 16, had just taken the first set 6-4 when Medvedev threw in the towel.

Medvedev had earlier received treatment from the physio, having seemingly struggled when moving to his right side.

"It's never easy in a match like this," Lehecka said. "If I were to choose the way how to win this match, it wouldn't be like that.

"So of course, it's never easy to see your opponent struggling, but at that moment, you just need to focus on yourself, trying to get the maximum level out of yourself."

Lehecka will face Felix Auger-Aliassime, who progressed thanks to a walkover following Jannik Sinner's withdrawal, for a place in the final.

Data Debrief: Czech mates

Lehecka is the third Czech player to reach the semi-finals in Madrid, following Jiri Vovak and Tomas Berdych.

Should Lehecka reach the final, he will move into the top 20 of the ATP rankings for the first time.