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We extend the methods of Davis-Januszkiewicz-Lafont to provide a newobstruction to smooth Riemannian metric with non-positive sectional curvature.We construct examples of locally CAT(0) 4-manifolds $M$, whose universal coverssatisfy isolated flats condition and contain 2-dimensional flats with theproperty that $\sqcup\ \partial^\infty F_i \hookrightarrow \partial^\infty\tilde M$ are non-trivial links that are not isotopic to any great circle link.Further, all the flats in $\tilde M$ are unknotted at infinity, and yet $M$does not have a Riemannian smoothing.

Link Obstruction to Riemannian smoothings of locally CAT(0) 4-manifolds