Italy's Olympic 100m champion Lamont Marcell Jacob says she will have to miss his sprint showdown with American Fred Kerly because of a back injury.
The pair were scheduled to race at a Diamond League meet in Rabat, Morocco on 28 May.
Jacobs said he had a "slight lumbar-sacral block that I plan to resolve as soon as possible".
He added: "Technically I feel fit and ready to have a great season outdoors. The challenge is only put on hold."
The next Diamond League event where the pair could meet is in Florence, Italy on 2 June.
Jacobs won a surprise gold when he beat Kerly to gold at the 2020 Olympics in Tokyo, which took place in 2021 because of the coronavirus pandemic.
He became the first Italian to win the title when he ran 9.80 seconds.
Kerly won World Championship gold last year when Jacobs was absent through injury.
