Captain Alun Wyn Jones looks set for a surprising return to the British & Irish Lions squad ahead of the series with the Springboks.
Meanwhile, Leinster and Ireland hooker Ronan Kelleher is poised for late call-up to Warren Gatland's squad.
Jones' tour looked to have been ended by a dislocated shoulder sustained in the Lions' warm-up victory over Japan at Murrayfield a fortnight ago.
The 35-year old wasn't on the plane to South Africa, but Gatland admits the richly experienced lock could make a late arrival.
"There's a possibility," the head coach said, as he revealed his side to play South Africa 'A'.
"He's back in training and we're waiting for the medical reports from him to see what happens with that."
Asked for further information on Jones' recovery, Gatland said, "A few weeks ago, we didn't think it [Jones returning] was an option.
"He's been back fully training with Wales. He's training this week with them and he's doing a double session with them tomorrow.
"We'll see what the outcome of that is.
"He's made a remarkable recovery. The assessment initially was that it wasn't as bad as they first thought but that's a real positive.
"It would be a boost to this squad, having someone of his experience and calibre to come back into the squad."
In Jones' absence, Conor Murray will again captain a strong Lions side for Wednesday's game in Cape Town.
The scrum-half is joined in the starting XV are his Ireland teammates Bundee Aki and Iain Henderson. Tadhg Beirne is names among the replacements.
Addressing rumours Ronan Kelleher could link up with the squad, Gatland said, "Players or replacement players would have to spend a number of days before they could join the squad officially.
“We are just looking at do we need cover at hooker, if we picked up an injury there, and then picked up an injury in training, they were concerned that possibly a game could go down to uncontested scrums.
"So we might look at making sure we have got some cover in the front row in terms of that hooker position.”
British & Irish Lions:
15. Anthony Watson (England/Bath), 14. Louis Rees-Zammit (Wales/Gloucester), 13. Chris Harris (Scotland/Gloucester), 12. Bundee Aki (Ireland/Connacht), 11. Josh Adams (Wales/Cardiff Blues), 10. Dan Biggar (Wales/Northampton), 9. Conor Murray (Ireland/Munster)
1. Wyn Jones (Wales/Scarlets), 2. Ken Owens (Wales/Scarlets), 3. Kyle Sinckler (England/Bristol), 4. Maro Itoje (England/Saracens), 5. Iain Henderson (Ireland/Ulster), 6. Josh Navidi (Wales/Cardiff Blues), 7. Tom Curry (England/Sale), 8. Taulupe Faletau (Wales/Bath).
Replacements: 16. Luke Cowan-Dickie (England/Exeter Chiefs), 17. Mako Vunipola (England/Saracens), 18. Zander Fagerson (Scotland/Glasgow Warriors), 19. Adam Beard (Wales/Ospreys), 20. Tadhg Beirne (Ireland/Munster), 21. Sam Simmonds (England/Exeter Chiefs). 22. Gareth Davies (Wales/Scarlets), 23. Elliot Daly (England/Saracens).
South Africa 'A':
15. Willie le Roux, 14. Cheslin Kolbe, 13. Lukhanyo Am (captain), 12. Damian de Allende, 11. Sbu Nkosi, 10. Morné Steyn, 9. Faf de Klerk.
1. Steven Kitshoff, 2. Joseph Dweba, 3. Trevor Nyakane, 4. Eben Etzebeth, 5. Franco Mostert, 6. Marco van Staden, 7. Pieter-Steph du Toit, 8. Jasper Wiese.
Replacements: 16. Malcolm Marx, 17. Coenie Oosthuizen, 18. Vincent Koch, 19. Nicolaas Janse van Rensburg, 20. Rynhardt Elstadt, 21. Herschel Jantjies, 22. Jesse Kriel, 23. Damian Willemse, 24. Kwagga Smith, 25. Elton Jantjies.