The British and Irish Lions will see how Alun Wyn Jones responds to a double training session on Tuesday before making a decision on whether to fly him to South Africa.
Jones' remarkable recovery from the dislocated shoulder that appeared to have ended his tour in the opening match against Japan on 26 June has reached a decisive phase.
If his shoulder withstands Tuesday's run-outs, he will rejoin the Lions squad in time for Saturday's clash with the Stormers.
Warren Gatland is likely to make a call on Wednesday morning once any after-effects from training are known.
"I know Al's doing some stuff back home and we'll obviously see how that goes first. I'm sure Warren will make a call when needed," kicking coach Neil Jenkins said.
"Nothing's beyond Al, there's no doubting that. He's an incredible person and player, on and off the pitch. He's incredibly diligent and works extremely hard.
"If he does get injured I know how hard he works to get himself back as quickly as possible.
"Nothing surprises me with Al and if he is able to join us at some point in time, it would certainly boost for him and everybody involved with the squad."
If Jones returns to the Lions squad it would be a stunning development that would catapult him into contention to start the first Test against South Africa in Cape Town on July 24.
Named as the original tour captain, the Wales skipper was replaced by Conor Murray when it seemed as though he would play no further part in the expedition against the world champions.
The Munster scrum-half took over the captaincy from Jones but the Welshman's possible return would raise questions around the role.
Murray is set to make his first start since being named Jones' replacement in Wednesday's clash with South Africa 'A’, with Ireland team-mates Bundee Aki and Iain Henderson also in the side.
Murray has two previous Lions tours behind him and is favourite to form a half-back partnership with Dan Biggar for the Test series.