  We consider the ratio of the top structure functions $R^{t}(\tau_{t})$ in top
pair production as a probe of the top content of the proton at the LHeC
project. We study the top structure functions with the geometrical scaling of
gluon distribution at small $x$ and show that top reduced cross section
exhibits geometrical scaling in a large range of photon vitualities. This
analysis shows that top longitudinal structure function has sizeable impact on
the top reduced cross section at $Q^{2}{\approx}~ 4m_{t}^{2}$.
