Novak Djokovic missed the semifinals of the ATP Masters in Rome.
The six-time tournament winner from Serbia lost his quarter-final against the Danish youngster Holger Rune (20) on Wednesday 2: 6, 6: 4, 2: 6.
Rune now meets Casper Ruud (Norway) or Francisco Cerundolo from Argentina in the semi-finals.
Djokovic, who will lose his leading position in the world rankings to Spaniard Carlos Alcaraz next week, struggled with back problems from the start.
He found the game difficult and gave up the first set after 38 minutes without a chance. The 35-year-old then reared up again under the influence of painkillers, but had to admit defeat after 2:19 hours.
Djokovic missed another prestigious tournament success before the highlight of the clay court season at the French Open (May 28 to June 11). In Paris, with his 23rd title, he wants to become the sole Grand Slam record champion.
His rival Rafael Nadal of Spain is undecided due to a persistent hip flexor injury.