The tweet says it all.
The Spanish FA released a statement on Friday.
"Sergio Ramos has left the squad on Friday morning after lumber pains that prevented him from playing the second half against Italy yesterday.
"Ramos will return to Spain today, while the national team continues to prepare for the second friendly that will take place on Sunday in Cluj against Romania."
He was subbed out at half-time in Spain's 1-1 result versus Italy. Nacho was subbed on for him, and will most likely get the starting nod against Romania.
This is one of the things that I and everyone else here never wants to see - an injury during International break. Those are some tough pills to swallow. Now Real Madrid have a Clasico in about 7 days, and our Captain has gone down with a back injury.