Marcell Coetzee's move to Ulster could be delayed after he suffered a knee injury while on duty for his current club the Sharks on Saturday.
The South Africa back row had to be carried off during the Sharks' 24-9 Super Rugby defeat by the Lions.
Coetzee, 24, was taken to hospital in Durban and Sharks coach Gary Gold admitted his concerns about the injury.
"It's not looking good. He's gone to hospital, he's had a scan," said the Sharks coach.
Coetzee, who has 28 South Africa caps, did not travel to New Zealand with the Sharks squad later on Saturday.
The Sharks will face the Blues, the Highlanders and the Chiefs in Super Rugby games in New Zealand over the coming three weeks.
The Springboks star is scheduled to join Ulster in the summer after the end of the Super Rugby season.
Coetzee, who has 28 South Africa caps, has signed a three-year deal with the Irish province.
Current Ulster number eight, Nick Williams, is leaving to join Cardiff Blues at the end of the season.