World Cup - Five pressing questions for USA vs. Portugal

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MANAUS, Brazil – Yes, Cristiano Ronaldo will play. No, Clint Dempsey will not wear a mask to protect his broken nose.

But some things can't be answered until the ball is kicked at Arena da Amazonia. Here are the most pressing questions going into United States vs. Portugal.

1. Who will replace Jozy Altidore?

Graham Zusi.

Jurgen Klinsmann adjusted the lineup to a 4-5-1, different than the 4-4-2 formation that he employed against Ghana. Aron Johannsson or Chris Wondolowski were candidates to take Altidore's place next to Dempsey up top, but Klinsmann chose to leave them on the bench.

Dempsey is more than capable of being a lone lead striker – he did so most notably with Fulham in the English Premier League – and he's strong enough to provide the back-to-the-goal dirty work that's so crucial to the U.S. attack.

2. How healthy is Cristiano Ronaldo?

The reigning World Player of the Year will lead the Portuguese onto the field wearing the captain's armband. The great unknown is how much of Ronaldo's superhuman fitness and skills will be on display due to a troublesome right knee.

The opening loss to Germany – an embarrassing 4-0 demolition – saw Ronaldo initially struggling to get in the game (and his teammates struggling to get him the ball). When he did get in a touch, he was immediately surrounded by multiple German defenders. Once hot-headed defender and Real Madrid teammate Pepe got red-carded for his head butt on German hat-trick hero Thomas Muller, Ronaldo could not hide his frustration and looked disinterested with every German goal that followed.

The U.S. certainly expects to see a more engaged and highly motivated Ronaldo on Sunday. The Americans sent effusive praise his way all week and the respect didn't stop at Saturday's press conferences.

Said Tim Howard, who played with Ronaldo at Manchester United: "He's the single hardest working player I've ever been around, on or off the field."

Rumors spread earlier in the week that Ronaldo was ignoring advice from his personal doctor to sit out the rest of the tournament. But Portugal midfielder Raul Meireles erased any doubt about his teammate's playing status by declaring Ronaldo is "fit to play."

"That's all I know," he said.

Ronaldo will remain a mystery until the 6 p.m. ET kickoff.

3. How bad will the conditions be?

According to Yahoo's weather app, the game-time temperature will be 81 degrees with a 40 percent chance of rain, likely thunderstorms. The muggy weather will be a challenge for both sides with players struggling late and fighting through leg cramps.

If it does rain, a slick pitch could have a less-than-100 percent Ronaldo treading carefully. But generally, wet conditions favor attackers because they can run at defenders who have little recourse to correct mistakes – they are always one slip away from disaster.

[Related: How weather in Manaus could be an advantage for U.S. team]

"If we play in the heat and humidity and we forget about the basic aspects of the game, we will have difficulties," Portugal coach Paulo Bento said.

Klinsmann will have the Americans prepared, mentally as well as physically, to slog through the sauna-like conditions for 90 minutes. It was this game location in the middle of the Amazon region that prompted him to value fitness so highly when choosing the final 23-man roster.

"We are full of energy," Klinsmann said. "We are very impatient. We can't wait to get this whole thing started."

4. Can Michael Bradley bounce back?

The belief that the Americans were still lucky to claim a 2-1 victory over Ghana stems from the fact that Bradley played poorly and struggled against the Ghanaians' physical play. There were long stretches where you didn't know if the Toronto FC star was on the field.

As the team's best box-to-box midfielder, Bradley must redeem himself for the U.S. to leave Manaus with a point or, the dream result, three points. Expect him to be his usual marauding self, making clean, hard tackles to regain possession and making pinpoint passes to create scoring chances for others.

5. Can the U.S. beat Portugal?

The Americans will face a Portugal side that is prepared to scratch and claw for its World Cup survival. The Portuguese are also missing four starters, including their most accomplished defenders in center back Pepe (suspension) and left back Fabio Coentrao (injury). A fifth regular, center back Bruno Alves (thigh), is a game-time decision. If he can't go, Luis Neto will take his place.

"We are prepared to fight," Bento declared.

[Yahoo Fan Shop: Suit up in Team USA World Cup gear]

The U.S. can't afford to counterpunch. It will need its outside backs, namely right back Fabian Johnson, to push Portugal back with attacking runs of its own.

"We have to be proactive. We have to make them defend," Howard said. "I think that's important."

Just as crucial is keeping the defense organized against the Portuguese pressure and that falls on Howard. The Americans don't stand a chance of winning if they don't get more blue-collar performances from center backs Geoff Cameron and Matt Besler and holding midfielders Kyle Beckerman and Jermaine Jones.