Speaking to Brazilian television outlet Globo Sport (h/t ESPN), the 22-year-old hints that this summer's tournament is a priority for him, which could affect the Blues' chances of winning the Premier League title:
We're aiming to try and play me in the final clash of the Premier League [against Cardiff] but I have to take care for the World Cup. We still have two very important games in the Premier League because Chelsea can still be champions, but it is important I rest because the World Cup is here.
I'm not playing because I felt a pain due to an injury to my hip, so, in the last game against Liverpool, I was not called on. I warmed up [against Atletico], but Mourinho knew that I could hardly play. Maybe I will not play the next game [against Norwich] because I could suffer a more serious injury to my hip and he knows it.
As things stand, Chelsea sit second in the Premier League, two points adrift of leaders Liverpool and just a point in front of Manchester City, who have a game in hand.
If all three teams were to win their remaining fixtures, City would most likely win the title on account of their superior goal difference of plus-58; Liverpool's is second-best at plus-50, and Chelsea's goal difference currently stands at plus-43.
Oscar has played in 32 of his side's 36 league fixtures this term, scoring eight goals and creating 46 scoring chances for his team in the process, the third-highest total of any Chelsea player, per Squawka.
BT Sport's Julien Laurens found it farcical that Oscar was not utilised in the 3-1 defeat to Atletico Madrid on Wednesday evening, where Jose Mourinho could have used the South American's talents as his side bowed out of the Champions League semi-final:
There isn't yet word on how severe the injury is, but the player's inclination to rest ahead of an international competition on home soil would appear to be affecting his involvement, as well as the actual injury itself.
Although Norwich and Cardiff are both threatened by relegation, Chelsea have already lost to Sunderland, Crystal Palace and Aston Villa this season and are fully aware of the threat that teams lower down in the standings can pose.
In Oscar's absence, Mourinho is likely to insist on playing without a central attacking midfielder and could instead opt for an extra presence in central midfield.
The likes of Eden Hazard, Andre Schurrle, Willian and Mohamed Salah will therefore have all the more pressure on their shoulders in providing the catalytic link between midfield and attack from out wide.
In order to guarantee their Premier League title challenge maintains its course, Chelsea need to take a maximum of six points from their remaining encounters, and Oscar will be a missed member of the squad should he have no further involvement.