The 22-year-old arrived at Stamford Bridge from Brazilian side Internacional back in 2012, and has established himself as a key player in West London since his £20m switch, forming an outstanding attacking trident with Eden Hazard and Juan Mata last season.
But this term, Oscar has had an up and down campaign, starting the season well before struggling to make an impact since the turn of the year, and his underwhelming displays haven't gone unnoticed by not only Blues fans but also manager Mourinho, who believes the midfielder has been disappointing of late but will rediscover his best form for the World Cup this summer.
"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 said. “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.
Mourinho has led a sustained title challenge in his first season back at Stamford Bridge, and has admitted that Oscar's compatriot Willian has improved the most under him this term, but called for improvement from Andre Schurrle ahead of next season, where the expectations around the club will be increased.
“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. 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," concluded Mourinho.