Thiago himself has recently made his choice to play for Spain by making his debut for their senior side, but admitted that his brother has a different opinion on the matter.
"It's a very personal decision. We each have our opinion on this matter. We might be brothers, but we feel different about this," Thiago was quoted as saying by Sport.
"We have to respect his decision, regardless of whether he chooses Spain or Brazil.
"It is a difficult decision for the family, because they want us to represent Brazil. It was a logical decision for me though to choose Spain. I had made up my mind at the age of 16."
Rafinha is currently 18 years old, and has played for Spain in their U-19 squad, but is still allowed to switch allegiances under FIFA regulations until he receives a senior cap.
He currently plays for Barcelona's B squad in the Segunda division as an attacking midfielder.