The UK agency has been gathering input and information for the past few month on allegations of rigging in the currency market, which has a daily volume of $5.3 trillion, according to people cited by the FT.
Any announcement by the SFO follows frequent information-sharing meetings with the UK's Financial Conduct Authority, the same sources said.
The SFO would not confirm or deny a formal probe would be announced. "We are receiving and examining complex data on this topic. If and when we open a criminal investigation, that decision will be announced in the usual way," the FT quoted the SFO as saying.
(Reporting by Gertrude Chavez-Dreyfuss; Editing by Andrea Ricci)