As it stands, the duo appear to be outside bets to be selected by coach Luiz Felipe Scolari, who opted not to pick them for the recent Confederations Cup.
However, right-back Rafael refuses to give up hope, telling United Review: "I dream to be there. I will just keep doing my job here and try to play well and sometime maybe it will happen."
Meanwhile, Fabio, who spent last season on loan at Queens Park Rangers, has admitted that while his chances may be slender, his brother should be included.
"If it doesn't, I will be writing a letter! I think my brother is good, but still the manager doesn't call him," he said.
"I dream as well, but for me I think it's harder. Last season I had a bad season – well, not a bad season, but the team didn't do well and that wasn't good for me."
The 23-year-olds have made two appearances each for Brazil at senior international level.