Altidore playing game of patience.
The USA striker was stretchered off with a hamstring injury in his country's opening Group G game against Ghana on Monday and he has been ruled out of tomorrow's game against Portugal.
A team spokesman said earlier this week Altidore may yet recover in time to play some part in the tournament.
However, Altidore remains cautious, saying: "I am not really setting any timetable to return.
"I am just focused on getting myself right and being the best cheerleader for the team.
"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 is just staying mentally prepared and doing the best I can to get on the field as soon as possible."
Altidore's injury struck in the first half of the win over Ghana, the 24-yearold pulling up clutching the hamstring on his left leg.
He added: "I am all right. I am a little bit sore but a lot better than I was Monday.
"It is one of those where I knew I could not continue as soon as I felt the muscle.
"So it was a little bit unlucky, but we have guys who are going to step in and do a great job for us on Sunday.
"The mood in the team is exciting. Everybody is excited, ramped up and ready to go.
"I think it is a good opportunity for us to get to the next round with a good result against Portugal."
USA striker Jozy Altidore