There were doubts surrounding the game after a member of the Lions management team in South Africa tested positive for coronavirus.
The Lions have now revealed that a player has also tested positive following a round of PCR testing.
The two individuals had a total of 12 close contacts – eight players and four staff members – and all have been placed into isolation at the team hotel.
All other members of the touring party returned negative results.
After consultation with the Medical Advisory Group (MAG), this evening’s game against the Sharks at Emirates Airline Park will still take place at the later time of 7pm BST.
But the Lions have been forced into make several changes to their matchday 23.
Scotland scrum-half Ali Price, who was not in the original 23, will start the match in place of Gareth Davies.
Price is the only recognised scrum-half in the matchday squad, with Conor Murray – who was named among the replacements – also dropping out.
There are now three Scots in the starting XV, with Price joining Zander Fagerson and Duhan van der Merwe.
Finn Russell comes onto the bench along with Hamish Watson but fellow Scots Stuart Hogg and Chris Harris drop out.
Other changes in the starting XV see Josh Adams replacing Liam Williams at full-back, Louis Rees-Zammit replacing Anthony Watson at right wing and Owen Farrell replacing Dan Biggar at stand-off.
Revised British and Irish Lions team
15. Josh Adams (Cardiff Rugby, Wales)
14. Louis Rees-Zammit (Gloucester Rugby, Wales)
13. Elliot Daly (Saracens, England)
12. Bundee Aki (Connacht Rugby, Ireland)
11. Duhan van der Merwe (Worcester Warriors, Scotland)
10. Owen Farrell (Saracens, England)
9. Ali Price (Glasgow Warriors, Scotland)
1. Mako Vunipola (Saracens, England)
2. Luke Cowan-Dickie (Exeter Chiefs, England)
3. Zander Fagerson (Glasgow Warriors, Scotland)
4. Iain Henderson – Captain (Ulster Rugby, Ireland)
5. Adam Beard (Ospreys, Wales)
6.Josh Navidi (Cardiff Rugby, Wales)
7. Tom Curry (Sale Sharks, England)
8. Sam Simmonds (Exeter Chiefs, England)
16. Ken Owens (Scarlets, Wales)
17. Rory Sutherland (Worcester Warriors, Scotland)
18. Tadhg Furlong (Leinster Rugby, Ireland)
19. Maro Itoje (Saracens, England)
20. Jack Conan (Leinster Rugby, Ireland)
21. Hamish Watson (Edinburgh Rugby, Scotland)
22. Finn Russell (Racing 92, Scotland)
23. Taulupe Faletau (Bath Rugby, Wales)