World No. 1 and U.S. Open champion Carlos Alcaraz will miss the Australian Open after suffering another injury.

The 19-year-old missed the end of 2022 with an abdominal tear, and has now sustained an injury to “the semimembranosus muscle in my right leg,” he posted on social media.

World No. 2 and 22-time major champion Rafael Nadal will become the No. 1 seed at the Australian Open, which starts Jan. 16. Novak Djokovic, ranked No. 5, will be the 4 seed, but figures to be the favorite.

“Novak is the solid favorite with or without Alcaraz, or anyone else for that matter,” ESPN’s Patrick McEnroe said by text. “Alcaraz is ranked No. 1, Djoker is the favorite.”

Alcaraz won the U.S. Open last fall — beating Casper Rudd in four sets — but hasn’t played since October when he retired against Holger Rune in the quarterfinals of the Paris Indoors.

In November, he became the first teen and youngest player in history to finish as year-end No. 1 (since 1973).

“It means a lot to me," Alcaraz said then. “To get this trophy, the World No. 1, to be part of tennis history along with a lot of legends, for me [it] is an amazing feeling.”

The Spaniard lost to Matteo Berrettini in the third round of the Australian Open last year.