The London club could yet claim the Premier League trophy this season should Manchester City and Liverpool slip up in their final two games.
However, Mourinho has repeatedly insisted his side will be better placed to compete for glory in the 2014-15 campaign.
The Portuguese was critical of Eden Hazard on Friday, suggesting the 23-year-old needs to do more from a defensive point of view to aid his team-mates.
Mourinho has now laid down the gauntlet to a number of his players, making his expectations clear.
"Willian has improved. But you can't succeed with everybody. At the end of the day, it’s up to them," Mourinho is quoted as saying by the British media.
"You try to help, but it’s up to them. Everyone who is in an age of improvement needs to improve. Everyone.
"Schurrle had a good season? Not bad, but next season must be better.
"Salah, Oscar, Willian, Hazard - all of them are in an age of improvement.”
Oscar's form has dipped in the second half of the season, with injuries a factor in the Brazilian's relative lack of impact compared to earlier in the campaign.
Mourinho added: "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.
"He arrived in the crucial moment of the season in a down. (He had) injuries, couldn't train, was trying to arrive to the game but didn't, was a doubt for the game, 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 whether he believed Oscar may be saving himself for the FIFA World Cup on home soil, Mourinho responded: "There are things you can't resolve."
