Nadal was leading the match 6-1, 2-0 when Correno Busta decided he had had enough.
Novak Djokovic beat Norway's Casper Ruud 7-5, 6-3 to collect a record-equalling sixth ATP Finals title on Sunday, earning the biggest paycheck ever in tennis - $4,740,300 - for completing the season-ending tournament unbeaten.
'I'm very privileged to be in the second week of Wimbledon again. This is genuinely one of my favourite weeks of the year so to be prolonging my stay is a lot of fun but I'm looking forward to the challenge.'
Monfils was playing in his first match in nearly seven months after the season resumed following the COVID-19 hiatus.
Play on Court Philippe Chatrier will have a familiar feel on Thursday with Rafa Nadal and Justine Henin, holders of eight French Open singles crowns, bidding to move into the third round.
Second seed Rafael Nadal said he would make no excuses after his shock loss to American Frances Tiafoe in the US Open fourth round Monday, despite a serious abdominal injury that derailed his run-up to the year's final major.
Novak Djokovic enjoyed success at his own tennis centre when he won the Belgrade Open with a 6-4, 6-3 win over Slovakian Alex Molcan in Saturday's final.
Stefanos Tsitsipas won 6-3, 6-3, 4-6, 4-6, 6-3 to book his place in the French Open final on Friday.
Images from Day 12 of the 2021 French Open at Roland Garros in Paris on Thursday.
French Tennis Federation (FFT) President Gilles Moretton described Osaka's action as a "phenomenal mistake".
'Neither I nor members of my team have symptoms of coronavirus. We carry out tests regularly. We will quarantine ourselves in accordance with current procedures'
IMAGES from Day 1 of all the action from the Wimbledon Championships played at the All England Lawn Tennis and Croquet Club, London, on Monday.
The fifth seeded German did not let up and another break confirmed the win in two hours and 40 minutes.
'When she hits her peak she's so dangerous because she moves well.'
Looking to improve her claycourt skills, she spent a bit of time at 11-time French Open champion Rafael Nadal's academy.
Factbox on Rafael Nadal, who beat Dominic Thiem 6-4, 6-3, 6-2 to win his 11th French Open title on Sunday:
Naomi Osaka has pulled out of the Wimbledon championship
It's on! Rafael Nadal and Novak Djokovic are set to clash in the French Open quarterfinal on Wednesday.
US Open champion Carlos Alcaraz has become the youngest world number one since the ATP rankings began in 1973.
Novak Djokovic kept his bid alive for Grand Slam No. 23 as he entered the semifinals of the French Open.
The Serbian's 1-6, 6-3, 6-1 defeat also ended his dream of winning an Olympic singles gold medal, the only major honour missing from his long list of accolades.
Five things to watch out for on day five of the French Open on Thursday
Images from Day 11 of the 2021 French Open at Roland Garros in Paris on Wednesday.
Federer decided to end his Roland Garros campaign on Sunday, a day after winning a gruelling third-round match against Dominik Koepfer.
Djokovic did not play badly in the final but it took him 55 minutes before he registered his first game in what turned out to be a mauling.
Images from Day 5 of the 2021 French Open, in Paris, on Thursday.
18-year-old Carlos Alcaraz entered the top 10 at the same age, on the same date and after a triumph in the same tournament as compatriot and 21-times major winner Rafael Nadal did in 2005.
'I have a lot of other goals, dreams that are in my mind and within my team and we'll certainly reset in the next couple of days ... enjoy some time together and then we go again. But really looking forward to the Olympics.'
The motto 'if at first you don't succeed' might have been coined for Japan's Yuichi Sugita, who after a battling French Open main draw debut on Sunday finds himself close to reaching the second round of a Grand Slam for the first time.
World number one Andy Murray will be ready for Roland Garros despite his poor recent form, nine-time French Open champion Rafael Nadal has said.
Rafael Nadal is chasing a historic 10th French Open title in Paris, but nothing will ever come close to trying to win his second.
World number one Novak Djokovic is on verge to become the first man to win US$100 million in prize money as he aims to book his place in the quarter-finals of the French Open for the 10th time.
Rafael Nadal, the king of clay won his 11th French Open title on Sunday.
Tsitsipas pulled out of the Wimbledon warm-up event in Halle, Germany, because of personal reasons
The moment Novak Djokovic accepted that being part of the Roger Federer/Rafael Nadal era was a chance, not a curse, everything improved for him.
Krejcikova became the first player to win both the women's singles and doubles title in Paris since Mary Pierce completed the feat in 2000.
Photos from the French Open matches played at the Roland Garros on Thursday
Monfils said all players were not similarly equipped to deal with the pressure of being a top athlete.
Holder Serena Williams survived her toughest challenge yet at this year's French Open as she battled into the fourth round with a 6-4, 7-6(10) win over Frenchwoman Kristina Mladenovic in a rain-disrupted match on Saturday.
Djokovic has won the last three editions of Wimbledon in 2018, 2019 and last year