A soft mattress may be behind the back injury that forced Brazil left-back Marcelo out of his country's 2-0 victory over Serbia, according to the team's medical staff.
Marcelo limped from the pitch early during Wednesday's game in Moscow, being replaced by Atletico Madrid's Filipe Luis, with the score still at 0-0.
Speaking in the Spartak Stadium's mixed zone after the game, Brazil team doctor Rodrigo Lasmar explained that the substitution had been a precaution as the 30-year-old had felt muscles "lock up" and knew he could not continue.
"Marcelo has a medical history with this kind of injury," Lasmar 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."
Marcelo has missed games for Real Madrid due to muscle problems in both of the last two seasons, with hamstring trouble in February 2018 and in January 2017.