Naomi Osaka retired from the Bad Homburg final due to a foot injury - just two days before Wimbledon.
The four-time grand slam champion was trailing Karolina Muchova 6-1 1-0 when she retired from the pre-Wimbledon warm-up.
Osaka had won four matches in a row this week, without dropping a set, showing good form as she reached her first grass-court final.
The 28-year-old was bidding to win her first title since the 2021 Australian Open, but was instead dealt a potential blow to her Wimbledon preparations.
Osaka had taken a medical timeout in the first set. Then, after gesturing she could not continue, she walked over to shake hands with Muchova and the umpire.
Osaka appeared in good spirits, however, as she addressed the crowd during the trophy presentation and congrulated Muchova for her victory.
The former world No 1 is seeded 14th at Wimbledon, and is scheduled to play her first-round match against Elsa Jacquemot on Monday afternoon.
The Japanese star, whose grand slam victories have come on hard courts, has never made it past the third round at Wimbledon in five previous attempts.
“I apologise for not being able to finish but this atmosphere has been incredible all week so thank you so much,” Osaka told the crowd in Germany.
“Congratulations Karolina, you’re one of the coolest girls on tour and it’s always fun to play. I hope you have the best of luck at Wimbledon as well.”
