The Spaniard is reportedly on the verge of joining the Blues' big rivals Manchester United. So with the Stamford Bridge hero all but out of the door, thoughts are turning to where Chelsea will invest the £40 million fee they will recoup from his sale.
Such adoration for graduates of the Toffees' academy system are becoming common place at Stamford Bridge. Last summer, it was Wayne Rooney, currently a Manchester United player, and now it seems Barkley has found his way into the Portuguese's thoughts.
It makes sense should Mourinho be chasing the 20-year-old. Similar to Rooney before him, he is a player who fits into the Chelsea manager's philosophy, demonstrating considerable physical attributes alongside his undoubted ability with a football.
There have been times this year when Barkley has looked anything but a rookie. Playing in his first full season as a first-team regular at Everton, it's what he is, though.
His marauding runs into opposition penalty areas have often left defenders fearing the worst—their whole persona suddenly becoming one devoid of composure and confidence when having to deal with him.
The Englishman enjoys imposing himself, and while he has the ability to pull off the majestic, he also isn't afraid to let his opponents know they are very much in a game.
It's almost Michael Ballack-esque.
Barkley is a long way off reaching the same level as the former Bayern Munich man, picked up by Chelsea on a free transfer in 2006, yet the fact remains his style and qualities are not too dissimilar.
Ballack was a juggernaut of a midfielder, a man who could mix it with the best and most feared midfielders throughout the continent.
Mourinho knew what he was getting when he persuaded him to move to Stamford Bridge. It will be the same with Barkley.
Indeed, with Frank Lampard's Chelsea career winding down, you could almost see Barkley's role for the Blues resembling a mixture of the duties Ballack and Chelsea's all-time goalscorer were asked to perform week in, week out during their time as a partnership.
And combining the two can only whet the appetite for what we could expect to see in the Premier League next term.
Besides all this, Barkley is English. Young Englishmen with his talents are a rare commodity in the top flight of English football, and with some big names on their way out sooner rather than later, Chelsea need to ensure they have their house in order when it comes to quotas.
Would Ross Barkley strengthen Chelsea's midfield?
The sale of Mata is going to be a painful experience for all involved at Chelsea—Mourinho, the players and fans. It's going to be where the pain will linger for some time, such was his reputation and impact in West London.
The Spaniard has been that good a player for the club, it almost seems surreal the Blues are allowing him to leave. And to Manchester United.
Mata was always doomed to failure under Mourinho, though. Not because he isn't talented, but simply because his style and approach are at odds with the qualities Mourinho likes to have throughout his squad.
He isn't an athlete in the same way Oscar, Eden Hazard and Willian are. He isn't an athlete in the way Barkley is developing.
Everton's young midfielder already has the look of a middleweight boxer about his person. It means he's able to not only charge through the proverbial brick walls for his manager but also crumble them to dust.
Players of his ilk are what Mourinho's teams thrive on.
Garry Hayes is Bleacher Report's lead Chelsea correspondent and will be following the club from a London base throughout the 2013-14 season. Follow him on Twitter here @garryhayes