The Real Madrid left-back was substituted after just 10 minutes of the game and early analysis suggested he was suffering from back problems.
Marcelo (left) was substituted due to a weird injury in Brazil's 2-0 win over Serbia.
But a day removed from Brazil securing passage to the last 16, Selecao's team doctor has shed some light.
"Injuries will happen, it's inevitable, and for the most varied reasons", he said Thursday, a day after the Brazilians advanced by beating Serbia. "The injury may be related to the hotel mattress".
There was good link-up play between Coutinho and his Barcelona teammate Paulinho for the opening goal with the former having found space in midfield before finding the former Spurs man who lifted the ball over the goalkeeper. "It was a spasm in the stabilising muscle and you can't play with that".
Marcelo consoled by his teammates.
It was Silva's header from a Neymar corner that ensured Brazil will take on Group F runners up Mexico in the round of 16 ahead of a possible clash with Belgium in the last-eight.
The Paris Saint-Germain forward, whose domestic season ended in February due to an ankle injury, recovered in time for the World Cup and scored his first goal in Brazil's 2-0 win over Costa Rica.
Will Brazil raise gold on July 15th?