"Whenever he's ready to let us know who's going to start, then he'll do it," the 23-year-old Icelandic-American said. "We just have to wait until he makes his decision."
-Carlisle: Filling in for Altidore
-Carlisle: CONCACAF showing well
-McIntyre: Klinsmann keeps plans private
-Labidou: Eddie Johnson backs Wondolowski
With Altidore out for Sunday's high-stakes match against FIFA's No. 4-ranked team (6 p.m. ET, ESPN/WatchESPN), Johannsson and Chris Wondolowski said Friday that they are ready to step in.
"It's a big loss losing Jozy, he's been playing really well and is in great form but I think our roles are going to stay the same," San Jose Earthquakes standout Wondolowski, who didn't play in the Americans World Cup campaign-opening 2-1 victory against Ghana, told reporters shortly before the team flew to the Amazonian city Manaus, the site of Sunday's game.
"I know for myself and Aron that we're both going to be ready to play at any minute and just looking for the opportunity and making the most of it whenever we get the chance."
Altidore pulled up lame 21 minutes into Monday's win, and was later diagnosed with a left hamstring strain. U.S. Soccer announced Thursday that the 24-year-old would not be available against Portugal, but could return later in the tournament. Altidore told ABC's "Good Morning America" on Friday that there was no timetable for his return.
Johannsson, who plays for Dutch side AZ Alkmaar -- Altidore's ex-employer -- replaced his former club teammate against Ghana but was largely ineffective.
Portugal also comes into the match facing lineup questions.
Fabio Coentrao (groin) and Pepe (suspension) are out. Fellow defender Bruno Alves, striker Hugo Almeida and goalkeeper Rui Patricio are questionable with ailments of their own. So is supertar forward Cristiano Ronaldo (knee), although the U.S. is preparing as if the reigning Ballon d'Or winner will be ready to go.
"We certainly expect that he's going to play," midfielder Michael Bradley said. "A game of this magnitude, of this importance for both teams, you'd always expect that the best players are going to find any way to be on the field."
U.S. in great spot against Portugal
Roberto Martinez and Santi Solari discuss the U.S. mindset heading into their match with Portugal.
Twellman: Altidore is irreplaceable
Taylor Twellman and Roberto Martinez think Jurgen Klinsmann will have to alter his tactics against Portugal due to the absence of Jozy Altidore.
No replacement for Altidore?
ESPN FC's Taylor Twellman joins The Herd and wonders if there is a replacement for Jozy Altidore if he is not fit.
Preparing for Portugal
The ESPN FC expert panel breakdown the United States' expected changes ahead of their vital match against Portugal.
Altidore: No timetable for my return
Jozy Altidore talks to "Good Morning America" about his hamstring injury.
All eyes on Klinsmann
The question of the day for the United States is: How will this team reconfigure itself following the lose of starter, Jozy Altidore?