Injuries sustained in last weekend's match against France have meant that Johnson will consider his options at training on Wednesday and Thursday before confirming the make-up of his back division and bench.
Meanwhile, among the forwards, the only change to the eight which started the 19-17 defeat to France on Saturday sees Ryan Wilson restored to the back-row in place of the injured Johnnie Beattie, with the experienced Alasdair Strokosch returning to provide cover on the bench.
Prop Alasdair Dickinson, who has recovered from the calf injury he sustained in Rome last month, and also returns to the substitutes.
But Johnson will now have to pick seven men from Chris Cusiter, Jack Cuthbert, Alex Dunbar, Max Evans, Dougie Fife, Stuart Hogg, Ruaridh Jackson, Lee Jones, Matt Scott, Greig Laidlaw, Duncan Taylor, Richie Vernon and Duncan Weir to start in Cardiff.
Tommy Seymour could join the group if he proves his fitness over the next few days.
Johnson - who will take charge of the side for the final time this weekend before Vern Cotter takes over in the summer - is definitely without wing Sean Lamont, who injured a knee against Les Bleus, while Evans has fitness doubts of his own.
Johnson explained: "We're obviously already without Sean Lamont in the backs after the knee problem he picked up against France.
"We've also got some concerns about our wingers, Tommy Seymour and Max Evans and we're going to wait until tomorrow to see how they are."
Options then could see Cuthbert, the 26-year-old Edinburgh Rugby back, who won his only cap to date in the 2011 Rugby World Cup warm-up match against Ireland, return to the fray.
Cuthbert made a strong impression in the Scotland A draw with England Saxons at Scotstoun in January, as did his Edinburgh Rugby team-mate Fife. The 23-year-old is unbeaten in two games for Scotland A against the Auld Enemy's reserves and has scored 10 tries for the Gunners in 41 appearances.
There is also Jones, whose last cap was against Ireland two years ago, but has been revitalised after a loan spell with Glasgow Warriors.