IRB Junior Player of the Year 2012 Jan Serfontein is the second key player in under a week to be ruled out of South Africa's squad for their title defence at the IRB Junior World Championship 2013 in France.
Serfontein has impressed in his Super Rugby debut season with the Bulls and has been part of the Springbok training squad which just concluded a camp in Durban.
His withdrawal from the JWC 2013 squad suggests he could be the latest Baby Boks star to graduate to the Test arena when South Africa host Scotland, Italy and Samoa for a four-team tournament next month.
Serfontein is replaced by Rohan Janse van Rensburg, who played for South Africa Schools last year and attended the Under 20 training camp two weeks ago as a reserve player.
The replacement means that fly half Handrè Pollard is the only member of South Africa's victorious JWC 2012 squad who will be part of the title defence in France, where the Baby Boks will face hosts France, England and IRB Junior World Rugby Trophy 2012 winners USA in Pool A.
The other player ruled out for South Africa is Sergeal Petersen, the wing who has shone fort the for the Southern Kings in their debut season in Super Rugby.
The flyer suffered a hamstring injury in the Kings' 72-10 loss to the Waratahs at the beginning of May but a MRI scan has shown that he will require a further three or four weeks rehabilitation.
Petersen has been replaced in the squad by former SA Schools utility back Jesse Kriel.