Argentina, led by the legendary Lionel Messi, faces a critical match with Poland as it attempts to qualify for the knockout rounds Wednesday.

Group C is tightly packed with Poland standing at 4 points, Argentina at 3 points and underdog Saudi Arabia at 3 points. Mexico is at the bottom of the table with 1 point, but it does have a chance of making the next round.

If Poland or Argentina wins outright, it will qualify for the next round. If Saudi Arabia defeats Mexico, it will also improbably make it to the knockout stages. But who advances otherwise gets more complicated from there.

Mexico needs to defeat Saudi Arabia if it wants to advance, but they still would need to get a helpful result in the Poland-Argentina match (either a Poland win or a draw and advantageous goal differential). A draw in both matches would put Argentina and Saudi Arabia tied at 4 points and come down to goal differential as well. Poland would win the group.

Group D is more clear. France has already qualified for the next round, so they may take it easy against Tunisia. Tunisia would need to beat France, get a draw in Australia-Denmark and win out on goal differential.

The Aussies would advance with a win against Denmark. Denmark can only advance with a win, though it would need a better goal differential than Tunisia if the African country upsets France.

Here is Wednesday's schedule:

U.S. star Christian Pulisic was taken to the hospital for scans on his abdomen after the team's win over Iran.

Pulisic sustained an injury after he slammed into Iranian goalkeeper Alireza Beiranvand while scoring the eventual game-winning goal late in the first half. Though he stayed down for several minutes and had to be helped to the sideline, he did return to the game.

The 24-year-old was substituted out at halftime. U.S. head coach Gregg Berhalter said immediately following the game he did not have an update on Pulisic's condition. The U.S.'s next game is Saturday.

President Joe Biden celebrated the U.S. win over Iran at the World Cup following remarks in Bay City, Michigan. He walked back up on stage and delivered his congratulations:

“USA! USA! That’s a big game, man. Well, I spoke to the coach and the players and said, ‘You can do it,'” Biden said.

He continued, “They did it. God love ‘em! Anyway, just thought you might want to hear.”

The U.S. will face the Netherlands at 10 a.m. on Saturday in the knockout round.

-ABC News' Ben Gittleson

The United States has advanced to the knockout stage of the World Cup with a 1-0 win over Iran.

Walker Zimmerman played hero for the U.S. in the 98th minute when he cleared a loose ball from just feet in front of their net.

The U.S. finished second in Group B and will face the Netherlands, the winner of Group A, in the knockout round.

Brazil and Portugal, two of the favorites to win the World Cup, are already into the knockout stage, but they'll have a chance to tune up for the second round in their final group matches on Friday.

In Group G, Brazil faces Cameroon, which needs to win and get a loss from Switzerland to qualify or a draw and better goal differential than the Swiss. Switzerland is facing off with Serbia. Serbia would need to win and get a loss by Cameroon or have a better goal differential. The Swiss just need a win or draw to advance alongside Brazil.

In the other set of games Friday, Portugal faces off with South Korea and Uruguay faces Ghana. Portugal may rest its top players, including Cristiano Ronaldo, so South Korea will be looking to take advantage and grab an upset win. Tottenham star Son Heung-min and South Korea need to win and get a loss from Ghana, or, if that game ends in a draw, beat Ghana in goal differential.

Uruguay, sitting on 1 point just like Korea, needs a similar situation. They'll need to beat Ghana and get a loss from South Korea, or beat Korea out on goal differential if the Portugal-South Korea match ends in a draw.

Here's the schedule for Friday, the final day of group play: