A standard Wiener sheet shifted by an unknown parameter is observed above a decreasing curve Γ. By the help of a direct discrete approach and under weaker assumptions than in the paper of Arató, N. M. [3], an explicit formula is derived for the maximum likelihood estimator (MLE) of the shift parameter. The MLE is a weighted linear combination of the values at the endpoints of the curve Γ and weighted integrals of the observed process and its normal derivative along the curve Γ.Keywords. Wiener sheet, Radon-Nikodym derivatives, maximum likelihood estimator, stochastic integral along a curve, weighted integral of the normal derivative of a random process along a curve.