Former Ospreys boss and Wales caretaker coach Johnson lost Sean Lamont, as well as back row Johnnie Beattie, to injury after the Round 4 defeat to France and he now has doubts surrounding wing duo Max Evans and Tommy Seymour.
While Beattie's absence with an ankle injury is easy to fix given the depth of Scotland's back row resources, the situation out wide is proving a little more problematic given that Lamont, Evans and Seymour have shared the wing duties in all four Championship games to date.
Evans was the obvious choice to step into ex-Scarlets star Lamont's shoes on Saturday but both he and Seymour will have to come through training today and tomorrow if they are to be named in the squad to face the reigning champions.
"We're obviously already without Sean Lamont in the backs after the knee problem he picked up against France," said Johnson. "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."
Johnson has therefore called up Lee Jones and Jack Cuthbert, as well as the uncapped Dougie Fife and former back row Richie Vernon, with the latter having been converted to a centre cum wing by Glasgow Warriors this season.
Vernon scored two tries for Glasgow against Leinster in the RaboDirect PRO12 a fortnight ago but has only started two games in the backs since he switched position earlier this season. Jones played in the Six Nations in 2012 but has since been loaned out to Glasgow from Edinburgh after spending time on the Sevens circuit. Cuthbert and Fife have been regulars for Edinburgh for most of the season, with Fife one of the leading try-scorers in the league, but Cuthbert is more often employed as a full back and Fife often features in midfield.
As a result, there are 13 players in contention for the seven backline places and three replacements spots at the weekend but Johnson has announced his starting forward pack and the five forwards who will sit on the bench.
The only change to the forward line up is that Ryan Wilson comes in for Beattie on the blindside flank, with British & Irish Lions tourist Ryan Grant having recovered from a hip problem to retain his place at loose-head prop.
Perpignan flanker Alasdair Strokosch is named among the replacements for what would be his first involvement in this year's tournament, while prop Alasdair Dickinson also features in the 23 having been declared fit again following the calf injury he sustained in the win over Italy last month.
Scotland backs from: Chris Cusiter, Jack Cuthbert, Alex Dunbar, Max Evans, Dougie Fife, Stuart Hogg, Ruaridh Jackson, Lee Jones, Greig Laidlaw, Matt Scott, Duncan Taylor, Richie Vernon, Duncan Weir
Forwards: 1 Ryan Grant, 2 Scott Lawson, 3 Geoff Cross, 4 Richie Gray, 5 Jim Hamilton, 6 Ryan Wilson, 7 Kelly Brown (captain), 8 David Denton
Replacements: 16 Ross Ford, 17 Alasdair Dickinson, 18 Euan Murray, 19 Tim Swinson, 20 Alasdair Strokosch, plus two backs