Brazil's team doctor has offered a bizarre excuse for why defender Marcelo was substituted during the country's final group match against Serbia on Thursday.
The 30-year-old limped off the field ten minutes into the Group E clash in Moscow.
Brazil went onto win the match 2-0, a win which saw it progress to the knockout stage.
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It wasn't until a post-match interview by team doctor Rodrigo Lasmar that the reason for Marcelo's substitution was revealed.
Lasmar said it was a precautionary measure because the defender felt his muscles "lock up".
"Marcelo has a medical history with this kind of injury," he said.
"Maybe it was the hotel's mattress, which was a bit more soft than usual. But [the injury] happened because he made a rotation movement and felt uncomfortable after. He could not continue in the game, because his muscles became locked up."
Marcel had previously missed games for his club side Real Madrid from back injuries.
Brazil coach Tite said: "I only know that he had a problem with his back. I know it was his back, more than that the doctor can explain. He said he locked up when he was leaving the pitch."
Brazil takes on Mexico in Samara on Monday to decide who progresses to the quarter final.
