The Brazil Under-20 international, Wallace Oliveira dos Santos, made his senior debut with the club earlier this year and has made 18 appearances since, helping the club win the Brazilian league championship.
At international level, the youngster was part of the Brazil squad that won the South American U17 championship last year. The 20-year-old was also part of the World Cup team in Mexico at the same level, finishing fourth in the tournament.
"Chelsea Football Club is delighted to announce we have agreed terms with Fluminense for the transfer of Wallace in the January window," a statement on the clubs official website said.
Fluminense is the club that both Deco and Juliano Belletti left Chelsea for in the summer of 2010.
Wallace will join a host of Brazilians in the Blues squad including Ramirez, Oscar, David Luiz and Lucas Piazon.