Green showed that, conditional on GRH, a subset $A \subseteq [N]$ with $\mid A \mid \gg_ε N^{\frac{11}{12}+ε}$ must contain two elements whose difference is $p-1$ for $p$ a prime. We prove an analogous unconditional result for $\mathbf{F}_2[x]$, improving the exponent to $\frac{7}{8}+ε$.