The 22-year-old has not seen any game time in the Blues' past three matches, although he was on the bench for both legs of the Champions League semi-final with Atletico Madrid.
Oscar explained after Wednesday's 3-1 defeat that his absence is due to a hip injury, which is likely to see him miss Sunday's Premier League encounter with Norwich.
The Brazil midfielder is hoping to be back for the season finale at Cardiff, but is wary of putting his World Cup place in jeopardy.
"I'm not playing because I felt a pain due to an injury to the abductor," Oscar told Globo Sport. "In the last game against Liverpool I was not called on.
"Yes, I warmed [against Atletico] but Mourinho knew that I could hardly play.
"Maybe I will not play the next game because I could get a more serious abductor injury and he knows it.
"We're treating me to try to play the final match of the Premier League, but I have to take care for the World Cup.
"We still have two very important games in the Premier League because Chelsea can be champions, but it is important to rest because the World Cup is here."
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- Premier League