Smalling enjoyed a fantastic campaign with United last season and the defender has put in strong performances during the ongoing European Championships as well, helping England make it into the knockout rounds of the competition.
Bilic has been left very impressed with Smalling's displays over the past year or so and has labeled the 26-year-old as one of England's best.
Bilic said on ITV: "For me, he is a top defender.
"To me, he looked shaky three years ago. But he's always quick and brave.
"Under Van Gaal last term, who obsessed over positions, he was great on the ball. Maybe not as attractive as say John Stones, but he passes the ball well.
"He's a leader, very quick on the ball. One of the best in England!"