GAON:
“If i recall… The Tosfos haRosh clearly states that a pirtzah greater than ten is only a rabanon. Hence, the above mentioned achronim did not see the tosfos harosh, as it was only recently discovered, one may say had they seen… they may have agreed.”
And so does the Hashlama and Haeshkol. However, the Mishkenos Yaakov (and Rav Aharon) claim some Rishonim maintain that pirtzos esser is d’Oraysa. (Rav Aharon adds Rabeinu Chananel.) However, the Bais Ephraim disagrees with these arguments. In any case, the three Rishonim that I mention Tosfos Rosh, Hashlama and Haeshkol, say clearly that the matter is only me’d’rabbanan, and the Mishkenos Yaakov did not have these sources.