This paper focuses on the effect of natural convection on the accuracy of diffusion coefficient measurements in concentrated liquid alloys. This convective effect is modelled using the concept of effective diffusivity, introduced in a former work for the case of dilute systems. Our computer simulations support the validity of this approach and show that it is very difficult in practice to reach conditions of negligible convective solute transport. The possibility of realizing the measurements of diffusion coefficients in microgravity is also discussed.