Mata has started just two games for the Stamford Bridge club this term, and was substituted on both occasions.
The two-time Chelsea player of the year was not even in the match day squad against Fulham at the weekend, and Minto believes the Spaniard must work harder to win back his spot amid fierce competition for places.
"They have an array of attacking midfielders at Chelsea," Minto told talkSPORT radio. "Personally, I'd like to see him play, he's been the best player for the last two years and now he can't even get a place on the bench.
"The ball is in Mata's court though. Jose Mourinho has thrown down the gauntlet. He has the chance to be a better player than he is at the moment, certainly a more complete midfielder, and that's wants Jose wants.
"You may question the way Jose Mourinho does things but he's decided Oscar can do what he wants all the time and Juan Mata doesn't. He's decided that if Mata is going to play in his side then he needs to work hard with the ball and without it."
Mourinho has identified Oscar as his preferred central attacking midfielder thus far, and the Brazilian international found the net against Martin Jol's Fulham on Saturday.
And with the likes of Willian, Kevin De Bruyne, Eden Hazard and Andre Schurrle all battling for three attacking midfield spots as well, Mata has plenty of competition to beat if he's to force his way back into Mourinho's thinking.
Following the Fulham victory, Mourinho said Mata remains part of his plans but admitted the Spain international must "adapt" his game if he's to be effective in the Chelsea boss's system.