England crashed out last night in defeat to the Czech Republic.
Keown told the Daily Mail: "Has impressed in each match and has improved no end since joining Manchester United from Fulham. I believe he has been working on his movement and he certainly looks more mobile than his central defensive partner Phil Jones.
"Smalling tried to take the game to the Czechs by bringing the ball out into midfield, which is a good option as he is more comfortable on the ball than many of those ahead of him.
"Smalling plays a high-energy game and has to make sure he leaves enough in the tank so players can't get in behind him with a sudden burst of pace."