Garnacho and Mainoo were two of United's bright sparks in a disappointing season in which they finished a worst-ever eighth in the Premier League era
Smith is the most successful captain in Test history and will seek in the new role to turn around the fortunes of an ailing South Africa side, who have lost their last five Tests in a row to Sri Lanka and India, two of which were by an innings.
Jacques Faul was appointed acting chief executive of Cricket South Africa last week after Thabang Moroe was suspended over governance concerns, and major sponsor Standard Bank decided not to renew their contract in April 2020.
"I am delighted that Graeme has agreed to assist Cricket South Africa up until the IPL next year," Faul said in a statement on Wednesday.
"Obviously, Graeme has had his concerns during the course of the last few months, but I am pleased to say that we have overcome those concerns and I look forward to working with him to urgently address pressing cricketing matters in particular.
"He is a natural leader and his knowledge of the game is second to none. To have him on board to work with the professional cricket arm of CSA, as well as the cricketing pipeline, which is so vital for our game, is a massive shot in the arm for CSA during this period."
The 38-year-old Smith said he was looking forward to making a positive impact over the next few months.
"I've publicly stated a number of times that I would love to assist CSA in this difficult time, particularly in developing this new role of Director of Cricket. I'm still as passionate about South African cricket as I ever was and I'm looking forward to getting stuck into the role.
"There is a lot of work to be done in the next few weeks and months and my objective will always be to make a positive impact during my tenure."
The first of four Tests against England starts on Dec. 26 in Pretoria.
Garnacho and Mainoo were two of United's bright sparks in a disappointing season in which they finished a worst-ever eighth in the Premier League era
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