Ruan Pienaar looks certain to miss Ulster's opening two European Champions Cup games next month after sustaining knee ligament damage in South Africa's defeat by New Zealand on Saturday.
Pienaar was injured in New Zealand's 14-10 Championship victory on Saturday.
South Africa coach Heyneke Meyer later said that the scrum-half is likely to be ruled out for six to eight weeks.
Ulster face Leicester in their European opener on 18 October before taking on star-studded Toulon a week later.
Pienaar's likely absence for Ulster will be a huge blow for a province who no longer can call upon Johann Muller, Stephen Ferris and John Afoa, following their departures from the club.
In addition, lock Iain Henderson has been ruled out for a couple of months because of a hip injury.
Scrum-half Pienaar was scheduled to be involved in two more Championship games for South Africa.
The Ulster star sustained the injury after an accidental collision with his South African team-mate Duane Vermeulen.
Pienaar has become a hugely influential player for Ulster since arriving at the Irish province in 2010.
He scored all Ulster's points in their European win over Leicester at Welford Road last January which ended the Tigers' unbeaten home run of 25 matches in the Heineken Cup.
Richie McCaw's 25th Test try helped New Zealand edge out the Springboks in Saturday's contest.
The All Blacks now have a six-point lead over South Africa in the table.
The two sides will meet again in the return fixture in the final round on 4 October.