Horn, who scored the SA U20s’ first try in their convincing 43-19 victory over Scotland in their opening match at the Racecourse Stadium on Tuesday, went for scans on his shoulder on Wednesday afternoon and the results confirmed that he had to return home.
Swanepoel, who plays lock for the Vodacom Blue Bulls, is expected to slot in with ease when he joins the team in Argentina on Friday, as he trained with the squad until one week before their departure for the international showpiece.
The experience he gained in the U20 International Series against Georgia and Argentina, and the Junior Springboks’ UK tour, where they faced England and Wales, means that Swanepoel will enter the tournament battle ready.
“I feel for Francke, especially after all the hard work he put in during the last few months to be at the World Rugby U20 Championship – he is a great player with fantastic character and leadership qualities,” said Junior Springbok coach Chean Roux.
“But injuries are part of the game, and we have a big task ahead, so it is great to be able to call on Janko, who played in our warm-up games and trained with us until shortly before we wrapped up our preparations at home.
“He was unlucky not to make the final squad of 28, and despite this, he continued to give his best at every training session before we left for Argentina. So I have no doubt that he will hit the ground running when he arrives and give everything at the tournament.”
Of the decision to replace Horn, who played at No 8 against Scotland, with a lock, Roux said: “We have sufficient cover at looseforward in the squad, and given the intense physical demands of this tournament with five matches in three weeks, it is important that we cover all our bases. Effective player management will be vital to work our way into a position to get into the final and give ourselves the best possible chance to win the competition.”
The Junior Springboks had a recovery day on Wednesday, while they also reviewed the Scotland match. They will return to the training field on Thursday where the focus will be on Saturday’s clash against Georgia.