World No 3 Alexander Zverev blamed illness after a last 16 elimination by Frenchman Alexandre Muller in the Hamburg Open on Wednesday botched his French Open dress rehearsal.
Muller, ranked 40th in the world, won 6-3, 4-6, 7-6 (7/5) to reach the quarterfinals, beating a top-five ranked opponent for the first time in his career.
The German struggled in the opening set, taking just two games as Muller won in 34 minutes. Zverev opened strongly in the second and broke his opponent twice.
In the third, Zverev and Muller broke each other once before forcing a tiebreak. Zverev held the advantage until Muller won the final three points to take the match.
A last-minute sign-up to the clay court event, Zverev had hoped to use his hometown tournament to gain momentum for the French Open.
The German said sickness was behind his lacklustre showing. "It was OK considering I threw up 37 times and had a fever of 39.4 degrees (Celsius, 102.9 Fahrenheit) all night.
"I was two points away from winning the match. There's a lot to be said in my favour."
The 28-year-old said his opponent had taken advantage of his poor condition.
"When I had to walk it was difficult. He then realised at some point I wasn't feeling well and made the points last as long as possible."
Still looking for a breakthrough Grand Slam victory, Zverev lost in the most recent Australian and French Open finals, along with the US Open in 2020.
After an inconsistent start to 2025, Zverev broke through to win the Bavarian Open in April, his third victory on the Munich clay. The German was however eliminated at the quarterfinals in Rome in straight sets last Wednesday.
Zverev won the tournament in 2023 and made the final last year, losing to France's Arthur Fils in a third-set tiebreak.
The German was considered the favourite for the tournament after world No 1 Jannik Sinner's late withdrawal.
Earlier on Wednesday, American second seed Frances Tiafoe was eliminated by Spaniard Roberto Bautista Agut and fourth-seeded Argentinian Francisco Cerundolo lost to Czech Jiri Lehecka.