Just days after Mourinho lambasted Eden Hazard for not being a 'team-player' in the light of his criticism of Chelsea's tactics, he has now admitted that Oscar was a disappointment to him in the closing months of the season.
"I think he was our best player for months, from August to November or December. He was absolutely fantastic. And after that he was up and down," Mourinho explained.
"He arrived in the crucial moment of the season in a down. Injuries, couldn't train, was trying to arrive to the game but didn't, was a doubt for the game, the game was too big to play with a doubtful player, so he arrived in the crucial moment of the season in a low.
"I can imagine, in a couple of weeks, he will be in a high and during the World Cup he will be in a high."
Asked if he thought Oscar's mind was already on the World Cup, Mourinho added: "There are things you can't resolve."
Mourinho was quick to highlight the improvement Willian has gone through this season and suggest the likes of Hazard, Oscar and Andre Schurrle need to follow his progress ahead of next season.
"Willian has improved. But you can't succeed with everybody. At the end of the day, it's up to them. You try to help, but it's up to them.
"You can help to build them. I'm not saying I'm going to succeed with every one of them. But, for example, I have Dr Biosca, who was the doctor in Shakhtar Donetsk for many years with Willian, and he says he doesn't recognise Willian: the professional, the player, the commitment, the ambition.
"The only thing he recognises is the talent because he has improved. You can't succeed with everybody. You try to help but it's up to them. Every one who is in an age of improvement needs to improve.
"You can't improve John Terry, Ashley Cole. If you keep them in the position where they are, it's fantastic. All of the others have to improve.
"Has Andre Schurrle had a good season? Not bad but next season must be better. Mohamed Salah, Oscar, Willian, Eden Hazard - all of them are in an age of improvement."
Reports in France claim that Paris Saint-Germain will step up their interest in Hazard and that they also have an interest in Oscar.