Balague, speaking on Revista de la Liga, said that the Real Madrid coach approached the South Coast club via a third person without the knowledge of Pochettino.
"Can I tell you a little story that not even Pochettino knows?" said Balague. "Jose Mourinho got in touch by a third person to the club to say 'you're not going to get it wrong with this guy, go for him'.
"It's interesting that Jose Mourinho took him under his wing for a little while and got in touch.
"Mourinho's put his own position on the line by going to Southampton and saying 'go for him'."
Pochettino's first job in management was at La Liga outfit Espanyol, where he was sacked in November following nearly three years in charge.