Brazil midfielder Oscar last night completed a switch from Internacional to European champions Chelsea, the English Premier League club said on their website.
According to British media reports, the deal is reportedly worth 25 million pounds.
The 20-year-old Oscar, in London on London Olympics duty, had long been linked with a move to Stamford Bridge but on Monday he had insisted his focus was entirely on winning Olympic gold.
Oscar dos Santos Emboaba Junior, to give him his full name, spent last season with Internacional of Porto Alegre, having started out with Sao Paulo.