Small momentum transfer elastic pion--proton cross-section at high energies is calculated assuming the proton is composed of two constituents, a quark and a diquark. We find that it is possible to fit very precisely the data when  (i)  the pion acts as a single entity (no constituent quark structure) and  (ii)  the diquark is rather large, comparable to the size of the proton.

PACS numbers: 25.80.Dj, 25.40.Cm, 14.20.Dh