The 21-year-old Plymothian was called into the England training party this week after Brad Barritt was ruled out of the remainder of the Six Nations campaign due to injury.
But Lancaster has opted not to have a look at the in-form Exeter Chiefs back this Saturday.
It is not the first occasion Slade has missed out this way and time is running out for him to force his way into England’s World Cup party.
However, fellow former Plymouth Albion loanee Jack Nowell will start for England on Saturday at Twickenham.
England team to face Scotland: 15 Mike Brown, 14 Anthony Watson, 13 Jonathan Joseph, 12 Luther Burrell, 11 Jack Nowell, 10 George Ford, 9 Ben Youngs, 1 Joe Marler, 2 Dylan Hartley, 3 Dan Cole, 4 Davie Attwood, 5 Courtney Lawes, 6 James Haskell, 7 Chris Robshaw, 8 Billy Vunipola. Reps: Tom Youngs, Mako Vunipola, Kieran Brookes, Geoff Parling, Tom Wood, Richard Wigglesworth, Danny Cipriani, Billy Twelvetrees.