We present a density functional theory to describe adsorption in systems where selected segments of chain molecules of fluids can bond (or associate) with functional groups attached to the surfaces. Association of active segments with the surface is modeled within the framework of the first-order thermodynamic perturbation theory. We discuss the influence of several parameters such as the density of surface active sites, the energy of association, the chain length, and the number of the active segment in the chain molecule on the structure of the fluid adjacent to the wall. The proposed model can be considered as a first step towards developing a density functional theory of molecular brushes chemically bonded to solid surfaces.