The 34-year-old ended his contract with the Red Devils at the beginning of the summer, opting to depart the club on a free transfer.
Newsonline report that Fabrizio Romano, said Mata would arrive in Istanbul in a couple of hours to sign a one-year deal with Galatasaray.
Galatasaray recently confirmed the signing of Mauro Icardi from Paris Saint-Germain on a season-long loan from the Ligue 1 champions.
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The Istanbul club which finished 13th in the Turkish Super Lig last season also signed Dries Mertens on a free transfer from Napoli and Lucas Torreira in a £5.5million deal from Arsenal.