Let \((M^n,g), n\ge 3\) be an asymptotically flat (AF) Riemannian manifold with nonnegative scalar curvature on which one of the Sobolev inequalities 0.1 \(\begin{aligned} \Big (\int _M|f|^pd\mu _g\Big )^{\frac{1}{p}}\le C \Big (\int _M|\nabla f|^qd\mu _g\Big )^{\frac{1}{q}}, \end{aligned}\) where \(f\in W^{1,q}(M), 1\le q<n\) and \(\frac{1}{p}=\frac{1}{q}-\frac{1}{n}\) , is satisfied with C the optimal constant for this inequality on \(\mathbb {R}^n\) , and suppose the positive mass theorem holds for AF manifolds, then (M, g) is isometric to \(\mathbb {R}^n\) .