SAO PAULO -- United States forward Jozy Altidore will miss Sunday's Group G World Cup match versus Portugal due to a strained left hamstring, the U.S. federation confirmed Thursday.

"He will not be available for Sunday's game, but we are hopeful he will be available in the tournament," U.S. Soccer spokesman Michael Kammarman said of the 24-year-old.

-Carlisle: Filling in for Altidore

-Carlisle: CONCACAF showing well

-McIntyre: Klinsmann keeps plans private

The Americans complete the group stage against three-time champion Germany on June 26. Aron Johannsson replaced Altidore after the 21st minute against Ghana. Chris Wondolowski is the other striker in the squad who could join Clint Dempsey in the attack.

A 31-year-old Californian, Wondolowski led Major League Soccer with 18 regular-season goals in 2010 and 27 in 2012, and tied for the lead with 16 in 2011.

"He can score from anything; score when you think there's nothing, no chance, and next thing you know he scores,'' Beckerman said. "He works his tail off for the guy behind him. He does a lot of things that don't show up on the stat sheet.''

Johannsson, a 23-year-old who was born in Mobile, Alabama, and grew up in Iceland, scored 26 goals last season for AZ Alkmaar in the Netherlands.

"Wondo is more the finisher in the box,'' Jones said. "Aron is more maybe the guy who's good with the ball and tries to go one against one.''

Coach Jurgen Klinsmann also could opt to shift from the 4-4-2 formation he used in the opener and start five midfielders.

"He's a big player for us,'' midfielder Kyle Beckerman said of Altidore. "We're extremely bummed for him and for the team, but we bring 23 players, and it's just a chance for somebody to step up. Hopefully the injury's not too bad and we can see Jozy later in the tournament.''

Kammarman did not reveal the severity of the strain. The Americans have just three days off between this weekend's game in Manaus and their first-round finale in Recife on June 26.

"It's bad news, but I think the team will handle this,'' midfielder Jermaine Jones said. "We have to handle that.''

Altidore left the Americans' World Cup opener against Ghana after straining his left hamstring in the 21st minute of Monday's 2-1 win against Ghana, leaving his status for the remainder of the tournament in question.

He was running down a ball with Ghana's John Boye when he lowered his head to attempt to control it, grabbed the back of his left leg and fell to the ground. Wincing in pain, Altidore was taken off on a stretcher.

Kammarman also said that Matt Besler should be available for Sunday's game in Manaus, and that Dempsey hasn't made a decision on wearing a mask. Dempsey scored 30 seconds into Monday's 2-1 win over Ghana, then was bloodied by a shin to the face from Boye when they battled for a header in the 33rd minute.

He added that the U.S. team travels with masks, so Dempsey wouldn't necessarily have to have one custom-made.

Besler exited the match against Ghana at half-time as a precaution after tweaking his hamstring.

Portugal also has issues after its opening 4-0 loss to Germany. Central defender Pepe was ejected after he appeared to head-butt Thomas Muller, right-back Fabio Coentrao was taken off on a stretcher and forward Hugo Almeida limped off. Pepe is suspended for Sunday's game, and Coentrao is out for the tournament.