Alexander Zverev has pulled out of the clay-court event in his native city of Hamburg due to back problems, opting for a few more days of rest ahead of the French Open.
The Hamburg tournament starts on Sunday, with the Paris grand slam beginning on May 24.
"I am really disappointed that I have to withdraw from the Bitpanda Hamburg Open this year. Hamburg is my home city and it is always something special for me to play in front of the home crowd," Zverev said in a statement on Friday.
"Unfortunately I have been struggling with back problems that have affected me throughout the clay-court season. My medical team has therefore strongly advised me to take a break from competition next week and recover."
Zverev, who has also recently been suffering from a cold, had already hinted at his decision not to play in Hamburg after his last-16 exit at the Masters 1,000 event in Rome at the start of the week.
After the withdrawal of defending champion Carlos Alcaraz at Roland Garros, Zverev is seeded second behind the all-conquering Jannik Sinner.
Despite Zverev pulling out in Hamburg, there are still several top names in northern Germany.
World number eight Alex de Minaur of Australia has confirmed he will play. Canada's Felix Auger-Aliassime and Ben Shelton of the US are also in the top 10.
