  We provide a fermionic description of flagged skew Grothendieck polynomials,
which can be seen as a $K$-theoretic counterpart of flagged skew Schur
polynomials. Our proof relies on the Jacobi-Trudi type formula established by
Matsumura. This result generalizes the author's previous works on a fermionic
description of skew Grothendieck polynomials and multi-Schur functions.
