Sergio Aguero was taken to hospital after fainting at half-time in Argentina's friendly defeat against Nigeria, the Argentinian Football Federation announced.
The Manchester City striker scored after 36 minutes in Krasnodar to put Argentina 2-0 ahead, but did not come out for the second half and was replaced by Dario Benedetto.
The Argentinian Football Federation stated in a Twitter post: "(Aguero medical bulletin) He fainted and was therefore transferred to carry out routine checks just as a precaution."
[PARTE MÉDICO AGÜERO] Tuvo un cuadro de lipotimia motivo por el cual fue trasladado a realizarse estudios de rutina sólo por precaución.— Selección Argentina 🇦🇷 (@Argentina) November 14, 2017
Speaking after the 4-2 defeat, in which Arsenal forward Alex Iwobi scored twice as Nigeria mounted a comeback, Argentina manager Jorge Sampaoli said on the federation website: "Sergio (Aguero) got dizzy and had to leave at half-time."
The developments in Russia are the latest health concerns for the City forward, who suffered a rib injury in a car crash in Amsterdam during October.
Initially it had been feared Aguero would be set for an extended spell on the sidelines, but the striker was soon back training and made a return to action for the Premier League match against Burnley, scoring the opening goal of a 3-0 win.
Aguero then went on to beat Eric Brook's goals record in all competitions for City, his strike against Napoli in the 4-2 away Champions League win on November 1 taking the forward on to 178.
The Argentina international joined City in a £38million transfer from Atletico Madrid during July 2011 and scored a dramatic stoppage-time winner to secure the Premier League title on the final day of his debut season.
Aguero, 29, still remains an integral part of Pep Guardiola's side, having scored 10 goals so far.
Unbeaten City have stormed clear at the top of the Premier League with 10 wins from their opening 11 matches and beat Arsenal 3-1 before the international break.
Guardiola's men resume their domestic campaign at Leicester on Saturday - when it remains to be seen whether Aguero will be passed fit to play.