The Bundesliga champions appear to be in pole position to lure the highly rated 22-year-old away from the Nou Camp, despite interest from Manchester United.
Reports earlier this week claimed the player had agreed a four-year contract at the Allianz Arena, but Sammer insists such suggestions are premature.
"Why would we not communicate it if something was signed? No, of course that is not the case," the 45-year-old told German newspaper Bild am Sonntag.
If the transfer did go through, it would see Thiago reunited with his former Barca boss Pep Guardiola.
New Bayern coach Guardiola confirmed on Thursday that Thiago, who came to the fore in Spain's triumphant European U21 Championship campaign with several fine performances including a stunning hat-trick in the final against Italy, was his number one transfer target this summer.
When asked at a press conference at the Bayern training camp if he was interested in Thiago, the 42-year-old said: "Yes.
"I don't know what's going to happen. We have to wait. I know him very, very well. He is a super, super player. He can play in three, four or five positions."
When asked about other transfers, Guardiola added: "It is either Thiago or nothing."