Shanghai SIPG general manager Sui Guoyang has claimed that Oscar decided to leave Chelsea due to becoming frustrated by his lack of first-team involvement under Antonio Conte.
The Brazil international will become the latest big-name footballer to join the Chinese Super League in January after agreeing a deal on a £60m switch to Shanghai, where he will team up with former Blues manager Andre Villas-Boas.
Oscar, 25, started Chelsea's first five Premier League matches this season, but has since been reduced to a bit-part player under new boss Conte, featuring regularly on the substitutes' bench.
Sui told Sky Sports News: "Oscar has fallen out of favour with Conte because he has no place in Chelsea's 3-4-3 formation. It played a key part in his desire to leave. He felt terrible to sit on the bench and not be involved. He is so young.
"Oscar wants to come back to the Brazil national team. Some of his compatriots play in the CSL and they still get called up to the national team. So it helped him to make the decision to move to China.
"And of course, the appointment of Andre Villas Boas is a plus. Oscar knows we are an ambitious club."