Blitzboks' Nel ruled out for London Sevens
The 24-year-old sustained the injury during their 29-19 Plate semifinal win over New Zealand at Stade Jean Bouin.
His lay-off will preclude him from playing in the last leg of the Series in London next weekend.
Albertus Smith was the other casualty for South Africa at the Paris tournament, the first to be played in the French capital in ten years.
The stalwart was ruled out on Friday already after picking up an ankle injury against England in the opening pool match.
The Blitzboks will be medically screened on Tuesday and the injury replacements will be announced thereafter.
It wasn't only injury woes served to the Blitzboks this past weekend; a 21-10 defeat against Samoa meant that South Africa missed out on a place in the top four for the first time since the opening tournament of the World Rugby Sevens Series in Dubai in December.
Despite being knocked out of Cup contention, Springbok Sevens coach Neil Powell was pleased with the way his team fought back.
"We did well against New Zealand and Australia," said Powell.
"This was not what we came for, but I cannot fault the guys on their effort in the last two matches."
Powell applauded Samoa's effort early in the day.
"We did not play well and they showed more urgency and composure than us and deserved the win," he said.
"It was disappointing, but I am pleased in the way we regrouped."
Although Fiji (166 points) extended their lead over the Blitzboks (152 points) this past weekend, the South Africans still have a chance to overhaul the the series-leaders in London, but the Blitzboks boss believes surpassing Ben Ryan's charges is highly unlikely.
"We are still in it, but to be honest, I can't see Fiji slipping up that badly next week in London," said Powell.
"We will of course still try and win both the tournament and hopefully the series.
“It will also be important to make sure that we at least finish second as it will help for a better draw come the Olympic Games.”
The South Africans' 17-7 Plate victory over Australia secured their second-place spot on the World Rugby Sevens Series log with one tournament to go.
Fiji top the log with 166 points, followed by South Africa (152) in second place and New Zealand (145) in the third spot.
Australia lie fourth with a tally of 127, while Argentina round off the top-five spots with 107.
Pools:
Pool A: South Africa, Samoa, USA, Canada
Pool B: Fiji, Australia, England, Wales
Pool C: France, Kenya, Scotland, Portugal
Pool D: Argentina, New Zealand, Russia, Brazil