The Manchester United midfielder is in the final year of his deal and is free to talk to clubs on the continent in January, with the Red Devils' board dragging their heels over an extension.
Mourinho stated earlier this week he wants Herrera to remain part of his squad and is hoping the money men will be able broker new terms with the combative Spaniard, who was the club's Player of the Year just two seasons ago.
Herrera had previously made it clear he was happy in Manchester but Barcelona's apparent interest could certainly make him think twice now.
Nou Camp officials were previously keen 18 months ago but United refused point-blank to countenance a sale of the former Athletic Bilbao man.
United, though, know Hererra is disappointed at being kept waiting on talks and now holds the whip hand in the negotiations.
The 29-year-old earns around £120,000-per-week and he can demand a substantial uplift, yet the lure of playing alongside Lionel Messi and a return to his homeland could make even United's deep pockets seem irrelevant at this late stage.