  We present a new test of gravitational interactions at the r\sim(0.2-20)Mpc
scale, around the virial radius of dark matter halos measured through
cluster-galaxy lensing of maxBCG clusters from the Sloan Digital Sky Survey
(SDSS). We employ predictions from self-consistent simulations of f(R) gravity
to find an upper bound on the background field amplitude of f_R0<3.5x10^-3 at
the 1D-marginalized 95% confidence level. As a model-independent assessment of
the constraining power of cluster profiles measured through weak gravitational
lensing, we also constrain the amplitude F_0 of a phenomenological modification
based on the profile enhancement induced by f(R) gravity when not including
effects from the increased cluster abundance in f(R). In both scenarios,
dark-matter-only simulations of the concordance model corresponding to f_R0=0
and F_0=0 are consistent with the lensing measurements, i.e., at the 68% and
95% confidence level, respectively.
