Argentina forward Sergio Aguero's World Cup future looks in doubt due to a muscle injury and the impressive form of potential replacement Ezequiel Lavezzi.
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Aguero, 26, has started all three of his country's games in Brazil so far, but was withdrawn after just 38 minutes of Wednesday's 3-2 Group F win over Nigeria, with a subsequent medical report stating he had "a muscle problem in his left thigh."
Lavezzi, 29, looked lively after being introduced in his place, making direct runs from a wide starting position, and leaving more space in the middle for Albiceleste captain Lionel Messi and centre-forward Gonzalo Higuain to exploit.
Argentina coach Alejandro Sabella would not confirm the seriousness of Aguero's injury in his postgame news conference, but did suggest that Lavezzi was in pole position to play in Tuesday's round-of-16 clash with Switzerland in Sao Paulo.
"El Kun [Aguero] had a muscular problem," Sabella said. "It will be looked at tomorrow. We will see. We have attackers who can play, or those who come in from wide. Lavezzi did not just make it difficult for them with his runs, but he also contributed to the team."
Argentina's performance against Nigeria was again mixed, with the attack functioning better than in earlier group games against Bosnia-Herzegovina and Iran, but some poor defending allowing Super Eagles winger Ahmed Musa to twice equalise.
Speaking with Ole after the game, Messi, who struck twice, said he was happy with how the team had played going forward, but conceded they could not afford to make such mistakes at the back once the tournament's knockout rounds begin.
"We forwards did not find these spaces in the previous games," the Barcelona player said. "We corrected that against Nigeria, so we were able to create more chances. But now we must work in defence to not concede goals.
"You cannot make mistakes now, because one game can leave you out of the competition. The good thing is we improved. We were playing against a team which has good players. You saw a good Argentina, but we want more."
Messi, who was substituted for Inter Milan's Ricky Alvarez with an hour of the game gone, said he had not been upset at the decision of his coach.
"We had spoken about it," he said. "[Sabella] said he would take me off, and he took me off. Now there are four or five days to recover [before playing Switzerland]."