The Brazilian football authorities coincided with the view of the courts in rescinding the player's link with Internacional, although the Colorado will fight to keep him
The 20-year-old Brazil international rescinded his contract unilaterally with the Tricolor in 2009, and Sao Paulo have always maintained that his move followed by signing with Inter constituted an illegal breach of contract.
The Regional Labour Court of the state found in his first club's favour this week, and an official bulletin from the CBF confirmed that they would be complying with the tribunal's judgement.
"With regards to the ruling made... in the case between Oscar and Sao Paulo, we inform that the athlete in question, from this date, no longer belongs to Internacional, given that the sporting link with Sao Paulo has now been re-established," the statement confirms.
Inter were forced to leave Oscar out of Wednesday's clash with The Strongest due to the decision, but club lawyer Rogerio Pastl affirmed that they would do everything in their power to keep their starlet in Porto Alegre.
"Inter will adopt a position, measures will be taken. Although we do not want to reveal everything, what I can say is that Internacional will pursue the preservation of their rights," the attorney explained in declarations published by UOL.
"What is certain, in this situation, is that Oscar will not be going back to Sao Paulo. He has no interest in that. Our constitution is on his side, no one shall be forced to work where they do not wish."
Inter are hoping that they will be able to pay a fine reportedly worth around R$5 million (€2m) the figure corresponding to his value when he left in 2009, to keep Oscar. Sao Paulo sources, however, have implied that the player's current worth should be reflected in any financial pay-off.