Daniil Medvedev lost in the opening round of the Halle Open as his grass-court campaign began with a shock defeat. The world No 2 is expected to challenge the big three of Roger Federer, Rafael Nadal and Novak Djokovic for Wimbledon glory.
Medvedev has been in fine form having reached the quarter-finals of the French Open for the first time before losing to eventual runner-up Stefanos Tsitsipas.
But his preparations for Wimbledon were dealt a blow as he lost 7-6 6-3 to world No 45 Jan-Lennard Struff in Halle.
Despite leading 5-2 in the first set and having set point, Medvedev could not close out the opener as his German opponent fought back to take the set on a tie-break.
Struff then broke twice in the second as he raced into a 5-1 lead.
Despite Medvedev recovering one of the breaks, he was unable to complete the comeback as Struff closed out the biggest win of his career.
Medvedev is the first player in 15 years outside of Federer, Nadal, Djokovic and Andy Murray to be ranked number two in the world.
His ranking will mean that he will avoid top seed and tournament favourite Djokovic before the final, but he could still face Federer and Nadal en route to a clash against the Serb.
The Russian reached the final of the Australian Open in February before losing to Djokovic in straight sets.
The 25-year-old is one of the young stars of the tennis tour and is widely viewed as a Grand Slam champion in waiting.
Wimbledon begins on June 26 and lasts for two weeks.
The tournament returns after a two-year break after the 2020 Championships were cancelled due to the coronavirus pandemic.