Lehecka, who had played a four-hour five-set match against Tommy Paul in the last round, took a timeout after the first set while a trainer treated blisters on his right foot.
The Czech, who produced 33 unforced errors in the match, struggled on through the second set but Medvedev broke his serve twice and was untroubled on his own.
"I feel sorry for Jiri because fourth round at Wimbledon, to get hurt it's not easy," Medvedev said in an interview on court. "He has a lot of Grand Slams ahead of him."
Wimbledon has been Medvedev's least successful Grand Slam tournament. The former world number one has reached four finals, winning the US Open in 2021.
He did not play at Wimbledon last year because of the ban on Russian competitors following Moscow's invasion of Ukraine, which Russia calls a 'special military operation'.
