World Cup winner Mata is to feature as Chelsea travel to Swindon in the Capital One Cup third round on Tuesday night.
Mourinho has told the Spain forward, who has made two starts this term after being near ever-present in his first two seasons at Chelsea, to prove his worth at the County Ground.
And Steve Holland has backed the Portuguese to further improve Mata, who was not in the squad for Saturday's defeat of Fulham and instead trained twice over the weekend.
Mourinho's assistant cited the example of Ronaldo, the world's most expensive player on his move to Real Madrid who improved his game still further at the Bernabeu.
"He (Mourinho) is always pushing, pushing the players to the maximum every day," Holland said.
"That's evident not just in his teams, but in the individuals he's worked with.
"If you look Jose's three-year period working with Ronaldo, he's really evolved as an individual. He's not just a talented dribbler and runner with the ball who can score goals.
"He has become a top-level match-winner who wants to run in behind, make runs, threaten the goal.
"I don't think that just happens. That comes with pushing, even if it's the best.
"On a day-to-day basis he (Mourinho) will be pushing for signs of improvement, working to progress the individual but ultimately for the benefit of the team."
Mourinho has spoken of a dislike of Chelsea's recent playing style and the project of adapting it.
With Oscar Mourinho's preferred playmaking number 10, the left-footed Mata is tasked with a wide right role which necessitates tracking back in defence.
Holland referred to Mata performing a similar role under Andre Villas-Boas in his first season at Chelsea following his signing from Valencia, before he was made the attacking lynch-pin under Roberto Di Matteo, a role he continued last term under Rafael Benitez.
"Having to adapt - and Jose has used that phrase - is nothing particularly new here," Holland added.
"It's another adaptation that is required. Juan has shown in his time here that he's more than capable of doing that. And I'm sure that will be the case this time."
As part of the style overhaul, Mourinho must manage a host of attacking talent in three strikers - Fernando Torres, Samuel Eto'o and Demba Ba - and six attack-minded midfielders players - Mata, Oscar, Eden Hazard, Willian, Andre Schurrle and Kevin de Bruyne.
When Mourinho brought Inter Milan to Stamford Bridge en route to winning the 2010 Champions League, Holland recalls an attacking quartet of Goran Pandev, Diego Milito, Eto'o and Wesley Sneijder who worked like "Trojans" defensively.
More recently at Real Madrid, Mourinho had a wealth of attacking talent at his disposal, too.
"The challenge, when the balance is loaded offensively like that, is that you don't just play with the ball, you have to play without the ball as well," Holland said.
"That's a challenge he (Mourinho) clearly managed to do (at Real Madrid), given the results that he had.
"He's quite clear in his mind, given the success he's had, what is his recipe for success. I'm quite sure that can be achieved here as well."
Mata did not make mention of his limited role so far this season in his blog, which is through the Chelsea website, instead focusing on winning the Barclays Premier League and Capital One Cup this term, having so far won the Champions League, FA Cup and Europa League in his two seasons with the Blues.
To win the League Cup, Chelsea must overcome Swindon at the County Ground in a challenge which is not to be underestimated, Holland says.
Holland pointed to recent precedent - Bradford's march to the final which included wins over Arsenal and Aston Villa, plus Liverpool's loss to Oldham in the FA Cup - as reason enough for Chelsea to be wary in Wiltshire.
"The warning signs are there," said Holland, reflecting on Chelsea beating League One Brentford in the FA Cup by virtue of a replay.
"If you think you've got a divine right just to turn up and win games, prepare to be surprised."