In order to fund the Johnson signing, which is believed to be costing Liverpool £18million, Benitez needs to sell.
Andrea Dossena looks to be off to Juventus for £7m and selling Arbeloa to Madrid would raise up to another £10m.
"Going back to Spain is always an idea that's in my mind," said the Spanish defender.
"I'm happy in Liverpool but I'd like to go back as I've barely had a chance to play in the top flight over there.
"It's always nice to be thought of by important teams, more still when it's this Real Madrid which Florentino (Perez) is building.
"They are making a big effort to build a great team. I have a year left at Liverpool but anything could happen.
"Certainly I will go back one day because, outside of football, I miss everything I have in my country."
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