The man South African coach Peter de Villiers has turned into his first-choice No 10 damaged his ankle ligaments in the 69th minute of his side's one point defeat in Durban.
And now Sharks doctor Craig Roberts has confirmed that Pienaar, whose father Gysie helped the Springboks to a 3-1 Test series triumph over Bill Beaumont's 1980 Lions, will be out of action for up to three weeks.
It means the talented Pienaar, who was given the pivotal role by De Villiers on last year's UK tour, faces a race against time to be fit for the first Test on 20 June.
Reuters reported Roberts as saying: "He has suffered a grade two sprain of his ankle ligaments. He had a scan today on the ankle and there is no other damage which is good news.
"It looks like he will be out for two to three weeks which is good news as he should be alright for the Lions series."
The 25-year-old Pienar has scored 62 points in 27 Tests for his country and has played in every position in the back line.