Manchester City boss Guardiola revealed the move last week when warning United against allowing Mata to come off contract this summer.
"Mata is a brilliant footballer. Previously Txiki (Begiristain) and I valued his incorporation at Barcelona, but finally we saw that despite his quality his signing was going to mean having to double up because we had (Andrea) Iniesta," recalled Guardiola.
And Mata confirmed: "Something came to me about the interest of Barça and it seems to me that the directors came to speak (to Valencia in 2011), but there was no contact with me."
Mata's father and agent was seen at Barcelona HQ last week.