"He shall surely be circumcised" (Genesis 17:13), the doubled expression is to include the shreds that hold back the circumcision [the remnants of foreskin that must also be removed]. "He has broken My covenant" (Genesis 17:14), to include the one whose foreskin has been drawn forward, by rabbinic decree, and the verse is a mere support. For Rav Huna said: By Torah law one whose foreskin has been drawn forward may eat of the priestly offering, but by their words [the sages] decreed against him because he appears as one uncircumcised.
The Shreds That Hold Back a Valid Circumcision
Yalkut Shimoni on Torah 82:3
הִמּוֹל יִמּוֹל, לְרַבּוֹת צִיצִין הַמְּעַכְּבִין אֶת הַמִּילָה. (בראשית יז יד) אֶת בְּרִיתִי הֵפַר לְרַבּוֹת הַמָּשׁוּךְ מִדְּרַבָּנָן, וּקְרָא אַסְמַכְתָּא בְּעָלְמָא, דְּאָמַר רַב הוּנָא, דְּבַר תּוֹרָה מָשׁוּךְ אוֹכֵל בִּתְרוּמָה, וּמִדִּבְרֵיהֶם גָּזְרוּ עָלָיו מִפְּנֵי שֶׁנִּרְאָה כְּעָרֵל.