U.S. forward Jozy Altidore said on Friday he does not know when he will be able to return to World Cup play after being sidelined with a hamstring injury during the United States' 2-1 win over Ghana on Monday.
"I'm not really setting any timetable [to return]. I'm just focused on getting myself right and being the best cheerleader for the team," Altidore said on ABC's "Good Morning America." "I think we have a lot of good players who are going to step in right away and do a great job for us. For myself, it's just staying mentally prepared and doing the best I can to get on the field as soon as possible."
U.S. coach Jurgen Klinsmann has given the team no word yet on who will replace Altidore in Sunday's Group G World Cup match vs. Portugal, said forward Aron Johannsson on Friday.
"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."
Altidore will miss Sunday's match against FIFA's No. 4 ranked team because of a strained left hamstring, the U.S. federation confirmed on Thursday.
"I'm all right. I'm a little bit sore but a lot better than I was Monday," he said. "It's one of those [injuries] where I knew I couldn't continue as soon as I felt the muscle. So it was a little bit unlucky, but we have guys that are going to step in and do a great job for us on Sunday."
All eyes were on Klinsmann during Friday's practice in Sao Paolo in anticipation of the naming of Altidore's substitute, but Klinsmann did not give any indication, Johannsson said. The Americans will 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.
Portugal is also ailing. The team's star forward, Cristiano Ronaldo, wore a knee brace during Friday's practice, as his left knee has been injured. The world player of the year was seen using an ice pack on it during training on Wednesday.
"Yeah, that might help a bit [if Portugal doesn't have Ronaldo]. He's a very good player. He's a guy that is world-renown for what he does -- somebody that can change a game on the drop of a dime. Whether he plays or not won't really take away from the challenge. But obviously, him not playing might help a little bit."
Klinsmann also could shift from the 4-4-2 formation he used in the opener and start five midfielders.
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.
"The mood [with the team] is exciting. Everybody is really excited, amped up and ready to go," Altidore said of the U.S.' training for Portugal. "I think it's a good opportunity for us to get to the next round with a good result against Portugal. The guys are excited, and they're up to the challenge."
Portugal has several other world-class players in its squad, but not all of them will be available for the match against the Americans. Defender Fabio Coentrao, Ronaldo's teammate at Real Madrid, has been ruled out of the rest of the World Cup with a muscle strain. And striker Hugo Almeida limped off midway through the first half against Germany with a muscle injury. Pepe, another Real Madrid defender, is suspended.
U.S. Soccer spokesman Michael Kammarman did not reveal the severity of Altidore's 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.
"Just like the Ghana game, I think there's going to be times where we're going to have to be on the front foot," Altidore said. "And other times, we're going to have to be defensively sound. Other times, pure will is going to have to get us through the game. I think we've been prepared for that over the years. I think Portugal will be another good opportunity for us to show that to the world."
Portugal lost 4-0 to Germany in their opening Group G match, with Ronaldo playing despite the injury.
The United States, however, are going in the other direction. After being knocked out of the last two World Cups by Ghana, the Americans beat the African team 2-1 in their opening match and could even secure a spot in the second round this weekend.
If Germany beats Ghana on Saturday and the Americans win on Sunday, Portugal and the Ghanaians will be eliminated.
Earlier this week, U.S. midfielder Michael Bradley told "Mike & Mike" that Portugal will be playing like a desperate team.
"It's a team that is going to be playing like their lives depend on it because their lives do depend on it," he said. "So we have to be ready to what the game is going to be about. Conditions will be hot and humid. We have to be ready to do everything we can to get another point, to get three more points and keep ourselves on a good roll."
Information from The Associated Press and ESPN FC's Doug McIntyre was used in this report.