Pulisic (calf) out of USMNT's clash with Australia...

United States star Christian Pulisic is out of the team's World Cup clash with Australia due to a calf injury, with Ricardo Pepi starting in his place.

Pulisic's status has been up in the air all week after coming off at halftime against Paraguay, and the AC Milan forward has been limited in training since. Just before the lineups were announced, coach Mauricio Pochettino confirmed his absence -- but that he is heading in the right direction.

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"Christian is not available," Pochettino said.

"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."

Pepi's introduction to the lineup hints at a tactical tweak by Pochettino, with the U.S. operating out of a 5-3-2. Pepi appears set to operate alongside Folarin Balogun, while Antonee Robinson and Sergiño Dest will be deployed as wingbacks.

The midfield trio remains the same with Weston McKennie and Malik Tillman flanking Tyler Adams.

The move also appears to be a response to what is likely to be a physical approach by Australia. When the two teams faced each other in a friendly last October, Pulisic was forced out of the match in the 31st minute after riding a heavy challenge.

His absence is a setback for a U.S. team that defeated Paraguay 4-1 in its opener on June 12 and with a win would clinch advancement to the round of 32.

Pulisic left the game at halftime after helping create the opening goal by splitting a pair of defenders before passing to McKennie, then setting up Balogun for the second goal.

Pochettino said the attacker was kicked in the back of his left calf during a training session ahead of the game and felt tightness during the match.

Pulisic, 27, trained on his own in the lead-up to the game against Australia.

Pulisic has 33 goals in 87 international appearances.

The U.S. will round out the group stage against Türkiye on Thursday at SoFi Stadium outside Los Angeles.

The Associated Press contributed to this report.