Eusebius (Εὐσέβιος) (d. c. 603) was a bishop of Thessalonica, Greece (then part of the Byzantine Empire), during the time of Pope Gregory I at the turn of the 7th century. He is best known for his polemical work of 10 books against a monk named Andreas, who had allegedly forged Greek-language books in Gregory's name that contained various falsehoods. Gregory stated in a letter to Eusebius that he neither spoke nor wrote Greek.
Little is known about Eusebius beyond this one matter.
George the shoemaker considered Bishop Eusebius to be a good man, but a very narrow-minded one. George knew that Eusebius would never approve of an alliance between the Christian citizenry and the ancient Greek demigods that lived in the wilderness, even though such was the only way to defeat the Avar-Slavic horde threatening Thessalonica. Behind Eusebius' back, George worked together with the liberal-minded priest Father Luke to make a pact with the ancient creatures. This protected the city against invasion, but Eusebius disapproved and assigned to Luke some strict acts of penance.