Marcelo limped off in the first half of Brazil's World Cup clash with Serbia, giving coach Tite cause for concern should they qualify for the last 16.
The Real Madrid left-back grimaced as he hobbled to the sidelines in the 10th minute of the Group E encounter, Filipe Luis coming on as his replacement.
Marcelo initially headed towards his team-mates in the dugout, but was helped down the tunnel by the medical staff in Moscow.
Filipe Luis only returned from six weeks out with a broken leg in May, and with Danilo struggling with a hip issue, Tite could find his options at full-back further restricted if Brazil make it to the last 16.
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