Warren Gatland will name his starting XV and bench for the Cape Town Stadium showdown on Wednesday morning, with tour captain Alun Wyn Jones expected to lead the side after recovering from a dislocated shoulder.
According to a report in the Times, three Scots will start, with full-back Stuart Hogg wing Duhan van der Merwe and scrum-half Ali Price selected to face the Springboks.
It would be a hugely significant moment for Scottish rugby as no Scot has started a Test match for the Lions on tour since Tom Smith in Australia 20 years ago.
Another two Scots are reportedly on the bench, loosehead prop Rory Sutherland and openside flanker Hamish Watson.
Hogg, van der Merwe and Price all impressed in the Lions’ 49-3 win over the Stormers on Saturday. Price in particular looked sharp, driving the team on by playing at a high tempo in Cape Town. His potential selection would see Conor Murray relegated to the bench after the Ireland scrum-half began the tour as captain.
The quicker than expected return of Jones from a dislocated shoulder has seen the Welshman reclaim the captaincy from Murray.
Hogg, the Scotland captain, is on his third Lions tour but things looked bleak for him at one stage when he was forced to isolate as a close contact of a Covid case. However, he returned to the side against the Stormers as captain and proved his fitness by playing the full 80 minutes.
Van der Merwe, who is a former South Africa Under-20 international, has scored five tries for the Lions and picked up two man-of-the-match awards on tour.
Sutherland and Watson have also impressed but, according to the report, Wyn Jones and Tom Curry are preferred as starters.
The Lions squad were informed of the team on Tuesday before the afternoon’s practice session at their base outside of Cape Town, which was the first opportunity for the starting XV to train together.
It is the most critical team selection of the tour as only once before, in 1989, have a Lions team lost the first Test but gone on to win the series.
South Africa named their team on Tuesday and captain Siya Kolisi has been passed fit to lead the side.
The flanker was one of 14 Springboks to test positive for coronavirus, forcing him to self-isolate in Johannesburg for 10 days.
Wing Makazole Mapimpi and prop Ox Nche have also been selected to start for the world champions in Cape Town this weekend, having also passed medical tests.
Fly-half Handre Pollard, another of the Springboks who tested positive, will win his 50th cap.
Possible British & Irish Lions team to face South Africa
S Hogg; A Watson, E Daly, R Henshaw, D van der Merwe; D Biggar, A Price; W Jones, L Cowan-Dickie, T Furlong, A W Jones, M Itoje, C Lawes, T Curry, J Conan.
Substitutes: K Owens, R Sutherland, K Sinckler, T Beirne, H Watson, I Henderson, C Murray, O Farrell.