The 20-year-old missed the plane to South Africa so that he could receive intensive physiotherapy at his club to remedy a troublesome thigh strain.
He was ordered to work with the Blues medical team to try to fully overcome the problem that first ruled him out of his club's Magners League clash with Munster prior to the tour.
But if he can prove there are no after effects from one final kicking session this week it is likely the Lions medical team will give him the all-clear to join them in time for the third game in Bloemfontein.
"Although I haven't seen Leigh since we were at Pennyhill Park he is doing very well by all accounts. He did a very good kicking session on Friday and he had a day off on Saturday," said Lions doctor James Robson.
"He is going to repeat his hared training session and also do some place kicking. I will be speaking to the Cardiff Blues doctor Geoff Davies about his reaction to the sessions.
"There will be further discussions but, if all goes well, we are looking to bring Leigh out in the middle of the week."
When he does arrive he will raise the Cardiff Blues contingent on tour to five it he will complete his dramatic rise from Blues Academy Player of the Year in 2008 to Lions Test candidate against the world champion Springboks a year later.
It has been an incredible 12 months for the man who will become the youngest member of the Lions squad when he arrives - inheriting the role of mascot carrier from the 21-year-old Munster and Ireland centre Keith Earls.
Halfpenny's Blues team mate Andy Powell is back in full training after missing the opening game with a hand injury. His hand blew up after taking a nasty bang and the doctors ordered him to stand down from the game against the Royal XV so as not to further aggravate the problem.
But he was back in the weights room on Sunday and is expected to be fit to play if required against the Golden Lions at Ellis Park on Wednesday. Irish back row man Stephen Ferris, who also pulled out of Saturday's opening game, is fit for consideration for Wednesday against the Golden Lions.
One player who won't be in the running for that game, though, is young Irish centre Keith Earls, who damaged his right shoulder in the first-half at Phokeng and will be out of training for up to three days.