The Spanish playmaker has been linked with a move to the Red Devils throughout the summer, with some sources claiming that a £17m deal was agreed in principle last week.
However, the Catalan giants have indicated that any potential transfer is far from completion by announcing that Thiago will return to them to prepare for next season
A Barca statement read: "We have the players we have and Thiago is one of them. Preseason with us begins as scheduled."
Thiago scored a hat-trick in Spain's European Under-21 Championship final triumph over Italy earlier this summer.