Medvedev, who was beaten by world number one Novak Djokovic in this year's Australian Open final, was elevated to second thanks to his win in the final of the Marseille tournament on Sunday.
Nadal was hampered by the problem at the Australian Open, where he was knocked out in the quarter-finals by Stefanos Tsitsipas.
The Serb reclaimed the top ranking from Rafael Nadal in February 2020 and finished as year-end number one for the sixth time, tying the mark set by Pete Sampras.
What was mind boggling was that Barty’s 1351 points lead over Naomi Osaka and 1931 points over Simona Halep was due almost entirely to tournaments she had played (and done well at) over a year before.
Top-ranked Ash Barty, who lost in the Australian Open quarterfinals, is the Adelaide defending champion.
The defeat left Medvedev, 25, a leading member of the next generation, wondering how to overcome Djokovic, Rafael Nadal and Roger Federer, who have 58 major titles between them.
A strict vegetarian diet, spiritual guru and family hugging-sessions are among the unusual methods that have helped Novak Djokovic to take his place among the immortals of tennis.
After refusing during the tournament to reveal the nature of the injury, he said on Sunday it was an abdominal muscle tear.
Here's a look at Djokovic's incredible run of success and the records he has set on the way to becoming the undoubted king of Melbourne Park:
Australian Open 2021: 'Brilliant work under pressure,' Twitterati react to Novak Djokovic's ninth title in Melbourne
Here's how Twitter reacted to Novak Djokovic's win over Daniil Medvedev in the Australian Open men's singles final.
Australian Open 2021: Novak Djokovic closes in on Roger Federer, Rafael Nadal with ninth triumph at Melbourne Park
In winning a third straight Australian Open for the second time, the Serb claimed his 18th Grand Slam title to move within two of Roger Federer and Rafael Nadal who have 20 each, while denying Medvedev his first.
Novak Djokovic’s Australian Open dominance improved to 18-0 combined in semi-finals and finals. On Sunday, Daniil Medvedev joined the ranks of Roger Federer, Rafael Nadal, Andy Murray, Stan Wawrinka, Dominic Thiem, all of whom have lost to Djoko in semis or finals in Melbourne.
Australian Open 2021 Highlights: Novak Djokovic claims ninth title in Melbourne with straight sets win over Daniil Medvedev
Australian Open 2021 men's final: Novak Djokovic heads into Sunday's Australian Open final unbeaten on eight previous occasions in the title match, but knowing he will need to be at his mental and physical best to overcome red-hot Russian Daniil Medvedev
23-year-old Naomi Osaka won her fourth Slam from the last eight she's contested. She became only the third player after Monica Seles and Roger Federer to win their first four major finals
Osaka's triumph over Jennifer Brady in the Australian Open final was hailed in Japan, and beyond, as astronaut Soichi Noguchi wrote from space "Naomi Osaka, congratulations on the victory," with a gold-medal emoji.
Australian Open 2021: Jennifer Brady says winning a Slam no longer feels as improbable as 'going to Mars'
Brady reached the Melbourne final despite undergoing 14 days' hard quarantine in Australia, forced to stay in her room while other players were allowed out every day to train.
The 23-year-old's zen-like mentality and increased gravitas on and off the court have elevated her alongside Serena Williams to being the one of the most recognisable female athletes on the planet.
"I'm probably going to watch some anime... maybe (eat) pizza... and go to sleep," said Osaka after winning her fourth Grand Slam title.
Naomi Osaka clinched her fourth Grand Slam title on Saturday after beating Jennifer Brady at the Australian Open. Here's how her two US Opens and two Australian Opens were won:
Osaka edged a tight first set but controlled the second to win 6-4, 6-3 in 77 minutes in front of thousands of fans at Rod Laver Arena.