Medvedev into first Wimbledon quarter-final after Lehecka quits
Medvedev was 6-4, 6-2 ahead when his 37th-ranked opponent, who had needed a medical timeout for a right foot injury, retired from their Court One clash.
Former US Open winner Medvedev will face either Stefanos Tsitsipas, the Greek world number five, or unseeded Christopher Eubanks of the United States for a place in the semi-finals.
"I saw that his movement was restricted but I didn't see that it was causing any real trouble," said Medvedev.
"But when I saw that he was retiring, I saw that it was different.
"I had no choice but to keep battling until the last point. I feel sorry for Jiri. Hopefully he'll recover and play at many more Grand Slams."