We present a scaling approach to the problem of a single chain in a good solvent between attracting walls that yields a simple analytical expression for the chain free energy as a function of the wall-to-wall distance, together with the amount of chain expansion parallel to the walls and with the effective layer thickness. Using the Domb-Gillis-Wilmers interatomic distribution function whereby the probability of a small interatomic distance r is (proportional to) r(theta), the method yields the critical exponents v and theta for the general dimensionality d through self-consistent optimization of the chain free energy. For d=2 we get v=0.707 and theta=0.828. An infinitely long, ringlike chain comprised between attracting parallel walls is investigated. Wall attraction on the chain atoms is effectively reduced by the solvent-mediated excluded-volume effect. The partition function is factorized into a bidimensional component projected on the walls and a monodimensional orthogonal component, using the thermal-blob concept. The resulting self-consistent free energy per monomer is a universal function of the effective wall-interaction free energy and of the wall-to-wall distance L. Remarkably, the numerical value of the exponents only affects the front factor of the free energy. Below the critical temperature T* at which wall attraction exactly compensates for the chain entropy loss at the wall boundary, the chain free energy attains a minimum at a wall-to-wall distance (L) over bar; below and above (L) over bar the walls are respectively repelled and attracted by the chain. The minimum originates from excluded-volume effects; if L is smaller than L the chain is merely squeezed by the walls, if L>(L) over bar it collapses on them with an increased compression, if L=(L) over bar it is pulled apart by the attracting walls, thus relieving the excluded-volume repulsion. At T=T* the distance (L) over bar goes to infinity, and at T>T* the repulsive force on the walls jumps to larger values, constant with temperature. Experimental measurements of the force exerted by polymer chains on confining surfaces, obtained by Klein and co-workers, appear to be consistent with these theoretical results.