Their results coming into Russian Federation weren't great and they were lucky not to lose by more than a goal to nil against Serbia on Sunday.
With a win Iceland could put Argentina on the brink of elimination.
Neymar started practicing with the rest of the squad but left accompanied by a doctor about 30 minutes into the session in Sochi.
Costa Rica did not get off to the start at the 2018 World Cup they hoped for, losing 1-0 to Serbia in their first group stage game. It had downplayed the seriousness of the injury, saying he was confirmed to play against Costa Rica on Friday in St. Petersburg. Costa Rica doesn't have history on its side: Brazil have won nine out of 10 matches against Costa Rica, with its only loss coming in 1960 friendly. Because of the number of fouls that he suffered in the last match he's felt some pain in his ankle, and that's why he's not training today.
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The Nigeria team is the youngest in the World Cup with an average age of just below 26, and although it is the most populous nation in Africa with some 185 million people, the team has never advanced past the round of 16. He was back with his team-mates on the practice pitch on Wednesday and took part in training at Krestovsky Stadium on the eve of Brazil's match against Costa Rica.
We will remind, the match ended with a draw 1:1.
"Neymar is one of the best players in the world and it's a great plus to have him in the team", said Philippe Coutinho, who has gained a bigger role as Neymar struggles with his fitness.
"We want to play well".
Switzerland came out with an impressive draw against Brazil and will look to keep the momentum going against Serbia.