United States star Christian Pulisic will sit out the team's World Cup match against Australia due to a calf injury, with Ricardo Pepi stepping into the starting lineup, head coach Mauricio Pochettino confirmed.

Pulisic's availability had been uncertain throughout the week after he was substituted at halftime against Paraguay. The AC Milan forward had been limited in training since that match.

"Christian is not available," said Pochettino. "The evolution is really well. Today he was training in the morning in the training camp. I think the feelings are good, I hope as soon as possible he will be ready to play again and be part of the team."

Pochettino said the 27-year-old was struck in the back of his left calf during a training session before the Paraguay match and felt tightness during the game itself. Pulisic trained separately from the squad ahead of the Australia clash.

The absence is a blow for a U.S. side that opened the tournament with a 4-1 win over Paraguay on June 12. A victory over Australia would clinch the Americans' advancement to the round of 32.

Before exiting at halftime against Paraguay, Pulisic split two defenders to set up Weston McKennie for the opening goal, then assisted Folarin Balogun on the second. Pulisic has scored 33 goals in 87 appearances for the national team.

Pepi is the lone change to the U.S. starting XI and will line up alongside Balogun, who scored twice against Paraguay. The Americans close out group play against Turkiye on Thursday at SoFi Stadium outside Los Angeles.