Wallace has been hotly-tipped for a move to Chelsea recently, but the deal has yet to be finalised according to the player's current club.
"Wallace has been negotiated for a long time," manager Braga told Terra. "He is a player that has impressed. Do you think people abroad sign someone based on one game?
"They watch a player for two, three months - sometimes even a year. They are taking a great player and Fluminense are completely right in selling him."
Fluminense's director Rodrigo Caetano confirmed that the paperwork has yet to be finalised.
He said: "I can't deny there are ongoing negotiations with Chelsea, but the deal isn't done yet, we still have exchange documents."
Wallace has been capped by the Brazil Under-17s.