Australian Nick Kyrgios said he "tried everything" to be fit after withdrawing from the Wimbledon warm-up tournament in Halle on Monday due to a knee issue.
The 28-year-old, who lost the 2022 Wimbledon final in four sets to Novak Djokovic, had surgery to repair a meniscus injury in his left knee in January.
"I tried everything here in Halle to be fit over the past few days, but I had to make the decision to pull out," Kyrgios said on Monday.
"When I play, I want to put in a performance like I did here last year when I was in the semi-finals, but that just wasn't possible," the Australian added.
Kyrgios, ranked 31, had been due to take on Italian Lorenzo Sonego on Tuesday morning in the German grass-court tournament, one of the most important lead-up events for Wimbledon, which begins on July 3.
Kyrgios complained of restricted movement after his first-round loss to Wu Yibing in Stuttgart earlier this month.
"I feel my knee every point. I can't walk without pain," Kyrgios said during the match.
With a 37-10 record, Kyrgios played the best season of his career in 2022, chalking up a tour-leading 12 wins on grass.
His place in Halle will be taken by 45th-ranked Russian Aslan Karatsev.
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