Responsa for Menachot 83:18

מידי הוא טעמא אלא לרב רב מיפסיל פסיל דאיתמר מנין למילה בעובד כוכבים שפסולה דרו בר פפא משמיה דרב אמר (בראשית יז, ט) ואתה את בריתי תשמור

This is permitted to be performed by a gentile, for it has been taught: In a town where there is no Israelite physician but there is a Cuthean<span class="x" onmousemove="('comment',' The Cutheans, often called Samaritans, were one of the peoples settled in Samaria by the Assyrian king after the exile of the ten tribes. They adopted certain Jewish practices, particularly those based upon the written word of the Torah; cf. 2 Kings XVII, 2ff. Later, however, they were found to be worshipping a dove on Mount Gerizim; v. Hul. 6a.');">¹⁸</span> physician as well as a gentile one, circumcision should be performed by the gentile but not by the Cuthean.

Teshuvot Maharam