Starting forward Jozy Altidore will miss Sunday's World Cup showdown against Portugal because of strained left hamstring, U.S. officials announced Thursday in Brazil.

The loss of the Americans' target forward will force coach Jurgen Klinsmann to re-configure the lineup when facing FIFA No. 4 Portugal in the Amazon.

The situation could lead to the World Cup debut for Earthquakes striker Chris Wondolowski, who didn't play in the opener against Ghana.

Aron Johannsson replaced Altidore after the injury Monday, playing 67 minutes against Ghana. But the Icelandic forward barely made a dent as Ghana controlled the game, particularly in the second half.

Defender Matt Besler, who left at halftime because of a sore right hamstring, should be available Sunday, a spokesman said. The spokesman added that Altidore could return before the tournament ends.

For the time being, Klinsmann must decide how to structure the lineup against the counterattacking Portuguese.

He might play with just Clint Dempsey up top and clog the midfield in an effort to choke off Portugal's favorite route to the goal -- through the handiwork of FIFA player of the year Cristiano Ronaldo.

Germany's midfield pressure stalled Portugal in a 4-0 defeat in the opener Monday.

"The No. 1 thing you cannot do against Portugal is when you lose possession, leave Cristiano Ronaldo open," ESPN analysts Taylor Twellman said.


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Portugal has lost striker Hugo Almeida and defender Fabio Coentrao for the rest of the World Cup after each suffered muscle injuries against Germany. The Selecao das Quinas also won't have central defender Pepe, who must sit out Sunday's game after receiving a red card for headbutting Thomas Muller.

"Jozy Altidore being out is much bigger than Pepe or Coentrão for Portugal if you ask me," Twellman said.

Portugal has its own major concerns regarding the health of Ronaldo. The star winger has been wearing an ice pack on a left knee throughout training and looked less than fit against Germany. He has suffered from tendinitis since the end of the Champions League campaign with Real Madrid.

Ronaldo left training early Wednesday, fueling rumors he won't be able to play against the United States. But coach Paulo Bento has said his midfielder is 100 percent fit.

Twellman, a former Major League Soccer star, said the biggest U.S. concern is Dempsey, who suffered a broken nose against Ghana.

"I'm not sure what Jürgen does, he has a couple decisions to make but I think first and foremost he has to find out what he gets from Clint Dempsey," Twellman said. "Everyone is talking Jozy out the door." But "Clint Dempsey has a broken nose. So, Clint and Jurgen need to figure out how much he can give, and in what spot does he need help up front."

Dempsey has not decided whether to wear a mask to protect his nose Sunday.

If Klinsmann goes with two forwards, his choices are Johannsson or Wondolowski, who bring different qualities to the field.

Johannsson, who was born in Alabama but reared in Iceland, is unpredictable, according to Klinsmann.

"An opponent will not know what he has in mind," the coach said last month at Stanford. "He sometimes thinks two or three moves ahead."

Johannsson, 23, scored 26 goals for the Dutch club AZ Alkmaar this past season.

Wondolowski, 31, has been one of Major League Soccer's best goal scorers for four years. He's not flashy but he scores with his feet or head.

"He's got that knack and real desire to be the one to win games for his team," former Quakes coach Frank Yallop said. "It is a hunger he has in him and it won't go away."

Contact Elliott Almond at 408-920-5865 and follow him on Twitter at twitter.com/elliottalmond.