The 38-year-old said he had been dealing with the injury throughout the tournament in Athens.
Daniil Medvedev has called for a streamlined ATP calendar with only Grand Slams and Masters 1000 tournaments offering ranking points, though the Russian concedes such reforms would be difficult to implement.
In the earlier match, Zverev beat Cilic -- the Croat's 9th loss in 10-round robin matches in the Finals
Stanislas Wawrinka returned to form with a 6-1, 6-1 thrashing of Tomas Berdych at the ATP World Tour Finals on Monday.
Japan's Kei Nishikori dispatched error-strewn Swiss Stan Wawrinka 6-2, 6-3 in a disappointingly one-sided clash at the ATP World Tour Finals on Monday.
American Jack Sock clinched the last spot in the ATP Tour finals when he beat Serbian qualifier 5-7, 6-4, 6-1 to win the Paris Masters title on Sunday.
World No 1 Rafael Nadal, who is hoping to recover from a knee injury to play in the season-ending showpiece, heads the other group and will face Belgian David Goffin, Bulgarian debutant Grigor Dimitrov and Austrian Dominic Thiem.
Stuns World No 1 Djokovic to win 'biggest title of career'
Belgian Goffin, thrashed by Grigor Dimitrov two days ago, appeared to be feeling the effects of that mauling as he went 3-0 down with a whimper, but came alive to win 15 points in a row during a first-set comeback.
Russian Medvedev, 29, last won a title at the Italian Open in May 2023 and has lost six finals since, including at the U.S. Open and Australian Open.
Rohan Bopanna and his doubles partner Florin Mergea qualified for the year-end ATP World Tour Finale when Vasek Pospisil and Jack Sock lost the Paris Masters final, on Sunday.
Wimbledon begins June 29 with Serena Williams returning after four years, Novak Djokovic chasing a 25th Slam, and a reshaped field after Carlos Alcaraz's injury.
Gael Monfils brought the party to Roland Garros on Thursday, teaming up with his wife Elina Svitolina to win a lively, star-studded exhibition match as he prepared for his final appearance at his home Grand Slam.
Wimbledon has announced a record 64.2 million prize money pot for this year's championships, a 20% increase from last year, marking the biggest annual rise in its history. This significant boost comes amidst growing demands from players for a larger share of Grand Slam revenues, with increases across all rounds and a substantial rise for singles champions and first-round losers.
The escalating conflict involving the U.S. and Israel with Iran has led to widespread disruption in the world of sports, with events postponed, travel plans thrown into chaos, and athletes seeking asylum.
The French Open will increase its prize money by 9.5% this year, bringing the total purse to 61.7 million euros. This increase reflects a broader trend of Grand Slam tournaments boosting player earnings, particularly in the early rounds, amid ongoing discussions about revenue distribution in tennis.
Photos from the ATP World Tour Finals matches played in London on Monday
Britain's Andy Murray joined world number one Novak Djokovic and newly-crowned US Open champion Rafa Nadal as definite qualifiers for the ATP World Tour finals on Tuesday, but Roger Federer faces an uphill task to make the eight-man field.
The Professional Tennis Players Association (PTPA) has criticised the French Open's prize money structure, supporting players' demands for a fairer share of revenue and broader structural changes in tennis.
Daniil Medvedev played down his Indian Wells semi-final win over Carlos Alcaraz, saying the Spaniard and Jannik Sinner remain on a different level from the rest of the ATP Tour.
Jannik Sinner, the world number one, showcased his dominance by defeating Alexander Zverev in straight sets to win the Madrid Open, marking his fifth successive ATP Masters 1000 title.
Jeevan Nedunchezhiyan and his partner Vijay Sundar Prashanth clinched their maiden ATP title together, winning the Hangzhou Open men's doubles event, while Yuki Bhambri and his French partner Albano Olivetti finished runners-up at the Chengdu Open
Tallon Griekspoor prevailed in a high-voltage three-set final against Benjamin Bonzi to win his maiden ATP World Tour title.
Jack Draper crashes out of Miami Open after loss to Reilly Opelka, while Ethan Quinn stuns Casper Ruud in a breakthrough win.
Six-time champion Roger Federer survived a late-night Swiss semi-final thriller against Stanislas Wawrinka on Saturday to set up an ATP World Tour Finals showdown against Novak Djokovic.
Jannik Sinner defeated Rafael Jodar in the Madrid Open quarter-finals, securing his spot in the semi-finals and becoming the sixth player to reach the semi-finals of all nine ATP 1000 Masters tournaments.
Eighth seed Machac, who won gold in mixed doubles at the Paris Olympics, became the third player from his country to win an ATP 500 title, following Tomas Berdych and Radek Stepanek.
Stefanos Tsitsipas' struggles continue with a first-round exit in Munich, as injuries and inconsistent form see his ranking drop to its lowest in eight years.
Frenchman Julien Benneteau caused a stir during an interview on French radio station RMC Sport on Sunday in which he said tournament referees were often kinder to Federer when it came to scheduling his matches.
Novak Djokovic has reportedly proposed to move the ATP World Tours Finals from London after 2015 by citing the need to expose the tournament to more cities around the world.
The 26-year-old has not always handled the expectations placed on his shoulders after he won the Wimbledon junior title in 2008 with a game style uncannily like Federer's.
Nikolay Davydenko beat weary Argentine Juan Martin del Potro 6-3, 6-4 to claim the ATP World Tour Finals title at the O2 Arena on Sunday. The wiry Russian, who has climbed to sixth in the world this week, produced a faultless display to claim the biggest title of his career and a $1.5 million cheque.
'We have exhausted all options for reform through dialogue, and the governing bodies have left us no choice but to seek accountability through the courts.'
India's Yuki Bhambri and his French partner Albano Olivett clinched the men's doubles title at the Swiss Open ATP Tour tennis tournament with a hard-fought win over Ugo Humbert and Fabrice Martin in the final in Gstaad
A simmering dispute between players and the Grand Slams over revenue sharing intensified at the French Open on Friday, with Novak Djokovic warning the sport risked further fragmentation as leading players pressed for a greater voice in shaping its future.
Roger Federer ended Grigor Dimitrov's seven-match winning streak and showed the Bulgarian he has some way to go to live up to his 'Baby Federer' tag with a 6-3 7-6 (2) quarter-final victory at the Basel Open on Friday.
The opening match in the Pete Sampras Group produced a feast of stylish backhands from both players but it was Dimitrov, the first Bulgarian to qualify for the tournament in its 48-year-old history, who overcome some late jitters to prevail.
Tumakuru, Karnataka, is set to host its first-ever ITF Women's World Tennis Tour W35 tournament, marking a significant moment for tennis in the region and offering a pathway for players to earn professional ranking points.
With world number four Ruud already assured of a semi-final berth the match was in reality a dead rubber.
Carlos Alcaraz beat his great rival Jannik Sinner 7-5, 7-6(8) to win their Hyundai Card Super Match exhibition event in Incheon, South Korea, on Saturday that marked the start of the season for the world's top two men's tennis players.
