Haven't seen any of him this season but based on his play the previous 2 when I saw a fair amount of him at Roma there has been a significant physical decline that would probably be a greater issue in England.
The bigger issue is how Smalling was consistently made a scapegoat for many of the issues in our play, with silly little meme's mocking the aesthetics of his game when his performances were strong over a number of years. He never had a consistent partner other than that spell with Blind, injury prone Jones, head case Rojo and Bailly, and finally the invisible man Lindelof. He was an easy target for criticism, the constant insistence that he was holding back our attacking play, and attackers, (the obsession with making excuses for the under performing star attackers contributes hugely here)
His peak years were genuinely excellent defensively.