Pienaar made his debut for Ulster against Glasgow on October 1 and has quickly become a fans' favourite with a series of impressive performances.
That form saw him named in the Springbok squad for the autumn Tests against all four Home Nations.
Pienaar joined up with his countrymen in Johannesburg yesterday and will return to Ireland on Wednesday as the Boks prepare for their opening clash with Ireland at the Aviva Stadium this Saturday.
The 26-year-old joins Racing Metro's Fancois Steyn as the only overseas-based players in the 30-man Bok party which will travel to the UK and Ireland without the likes of skipper John Smit, Jaque Fourie, Wynand Olivier, Andries Bekker, Fourie du Preez, Heinrich Brüssow, JP Pietersen, Gurthrö Steenkamp and Butch James.
Pienaar's Ulster team-mate BJ Botha was another player to miss out on selection due to injury.
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