Garbine Muguruza confirmed that a recurring back injury was to blame for her withdrawal from the Stuttgart Open on Thursday.
The Spaniard did not appear hampered in her movement despite losing the first set of her second-round match against Anastasia Pavlyuchenkova after dropping her serve in game 12.
But before the players returned to the court for the second set, Muguruza rose from her chair and shook hands with her opponent before leaving the arena.
Muguruza's retirement did not go down well with the Stuttgart crowd, who shortly beforehand had seen home favourite Angelique Kerber bow out with a thigh injury at 6-0 2-0 down to Anett Kontaveit.
"I'm disappointed, because this tournament, I never do really great results, and to retire, it's always bad for my Muguruza team," said the Wimbledon champion.
"I've been feeling my lower back since the Fed Cup, more or less since I started playing on clay, and I rushed a little bit here."
"It was a surprise for me as well, because I think we both started the match quite well, and I didn't know she was hurt," added Pavlyuchenkova.
"I felt like I was playing good, and I was in the zone. That's not the best way to win the match, but it is how it is, and I'm so very happy to be in the quarter-finals."
Like Muguruza, Kerber revealed that she had also come into the tournament with a pre-existing condition.
"I was feeling it a lot in the warm-up," said the 2015 and 2016 champion. "It started a few days ago, but this morning, I was feeling it more and more.
"I was trying everything to go out there. I'm here in Stuttgart, my home tournament, so I was trying everything, thinking I could play for the fans.
"At the end, it was too much and I started to feel the pain a lot in the first two games, where maybe I was sliding a little bit differently.
"It's more because of the pain. I played a good match on clay court yesterday, so I'll try to take that feeling back home with me, so I can learn from yesterday's match. I'll try to forget today as soon as possible, but I did my best to go out there in front of my home crowd.
"Now, we have to see what is going on: how bad it is and how long it will take to be 100 per cent again."
|Duminy encouraged despite South Africa´s mixed results|
|Thiem withdraws from Cincinnati Masters|
|Edwards joins Ospreys in consultancy role|
|Former Arsenal and Barcelona player Song joins Sion|
|I´m very happy with what I have - Spalletti not desperate for Modric|
|Roethlisberger evaluated for concussion after practice|
|Brady ´absolutely´ expects to face Eagles|
|Rugby Championship 2018: Reasons for optimism and concern for Australia|
|Wentz ´gonna be close´ for Eagles opener|
|Cleveland ´victory fridges´ to unlock beer if Browns finally win|
|England´s Watson suffers injury setback|
|Mariners reinstate Cano after 80-game suspension|
|AEK Athens 2 Celtic 1 (3-2 agg): Rodgers´ men dumped out of Champions League|
|Alonso to leave F1: Paddock reacts to Spaniard´s exit|
|Roma sign midfielder N´Zonzi from Sevilla|
|Alonso to leave F1: Who will replace Fernando at McLaren?|
|Extraordinary Zidane is in Real Madrid´s past - Lopetegui|
|Alonso to leave F1: Then and now - how the grid, teams and calendar have changed since 2001|
|Wawrinka and Azarenka receive US Open wildcards|
|Parma sign Napoli pair Inglese and Grassi on loan|
|Sandakan castles Proteas before Sri Lanka squeeze home|
|Ronaldo sale won´t stop Real Madrid winning - Ramos|
|Predators sign Ryan Ellis to eight-year, $50M contract|
|Curran, Woakes, Rashid - who makes way for Stokes in England´s Test XI?|
|Griezmann well positioned for Ballon d´Or, says Simeone|
|Criscito: I was on Genoa bridge shortly before collapse|
|Alonso to leave F1: How the Spaniard´s numbers stack up to the greats|
|Rookie LB Roquan Smith finally signs Bears contract|
|De Villiers enjoying relief from ´unbearable´ Proteas pressure|
|Fernando Alonso to leave F1|
|Spalletti extends Inter contract|
|Godin, Koke, Griezmann and Juanfran named Atletico Madrid captains|
|Ronaldo out of hospital after illness|
|Fury: Beating Wilder and Joshua ´very easy´|
|Dickinson retires to take up academy coaching role|
|Cricket the ´sole focus´ for Stokes as he returns to England squad|
|Cheryshev moves to Valencia on loan|
|Mandzukic retires from Croatia duty after World Cup|
|Ben Stokes found not guilty of affray|
|Tottenham issue new stadium update and apology to fans|
|Chelsea flop Bakayoko moves to AC Milan on loan|
|Gabi urges Al Sadd team-mate Xavi to play on|
|Ronaldo leads UEFA Goal of the Season nominees|
|Federer: Djokovic could be caught up in US Open pressure|
|Ronaldo to Juventus a huge boost for Serie A – Matthaus|
|Werner would welcome Ozil Germany return|
|´Perfectionist´ Serena admits to ´unrealistic´ expectations in tennis and motherhood|
|Klopp praises Deschamps and his ´boring´ France|
|LaLiga 2018-19: Bale or Griezmann - Who will step into Ronaldo´s breach as Messi´s main rival?|
|Woods winning 15th major would be greatest comeback in sport – Faldo|
|Retiring Storm great Hoffman not giving up on Finals dream|
|Folau won´t change aerial approach in All Blacks showdown|
|Racism behind Sterling criticism, says ex-Arsenal star Wright|
|Eto´o joins Qatar SC following Ligue 1 links|
|UEFA Super Cup 2018-19: Atletico academy eclipsing Madrid, La Masia|
|UEFA Super Cup 2018-19: Should Real Madrid cash in on Modric?|
|Scintillating Serena sends warning, Azarenka survives opener|
|DeGrom strikes out 12, Mets hit 5 homers in win over Yankees|
|Djokovic needs nine MPs as Murray crashes out|
|Murray unsure of US Open readiness after Cincinnati exit|
|Van Dijk: Alisson making difference at Liverpool|
|Johnson saves eight MPs but Djokovic prevails|
|Federer anxious ahead of Cincinnati comeback|
|Tevez relishing Messi reunion|
|Ronaldo arrival has taken Juve forward in Europe – Nedved|
|Serena steamrolls Gavrilova in Cincinnati return|
|Packers QB Rodgers doesn´t regret criticising team-mates|
|Indians OF Martin recovering from life-threatening bacterial infection|
|Shoulder injury sends Royals starter Duffy to DL|
|Yankees place Sabathia on DL with right knee inflammation|