SAN JOSE, COSTA RICA—Jozy Altidore wore flats to training on Wednesday. According to Jurgen Klinsmann, his status remained up in the air on Thursday.

"We take it day by day. Today will be another big step. Everything is healed with the hamstring issue. We did MRI. We did tests. Nothing can happen but he hasn't trained in a full rhythm for seven, eight days," the coach said.

(Graham Zusi, on the other hand, is 100 percent fit.)

If Altidore can't go, Aron Jóhannsson could get the call. His rapid introduction to the U.S. squad might seem surprising, but the American coach expected his newest forward to fit in.

"We were hopeful that his adjustment, becoming part of this team was going to go quickly. We were communicating for a year and a half about that moment. We would have had him to January camp already if it wasn't for his groin surgery," Klinsmann said.

"We always looked at him already as our player even if Iceland wanted him to represent the country. He gives us an element. He's a different type of a striker. He's a different type of a player. He takes people on. He's very light on his feet with his speed. But he always knows where the goal is, even if he's just roaming around with his back to the goal."

He continued: "We knew that once we get him, step-by-step here, and we give him some time to adjust, he will give us a different element. It's really nice to see. He's very focused. He knows what he wants. He wants to go to the World Cup."

The Americans enter Friday's match with eight players on yellow cards, but it wouldn't affect their strategy.

"It doesn't condition our lineup. It's about Costa Rica. It's about that game. Whatever happens Friday night, we will adjust to the Mexico game. Is it ideal? No. It's eight guys. That situation is not an easy thing but we'll take it the way it is. We're not holding back by any means," he said.

"I said it before," he continued, "I thought it was quite unfortunate for CONCACAF to give us a Mexican referee for the game because we play Mexico four days later. He has a big say in the game. But we respect him. From our end, we will do everything to make it a great game, a fair game. Maybe CONCACAF next time thinks about it first."

Noah Davis is American Soccer Now's deputy editor. Follow him on Twitter.