Duane Vermeulen's Ulster debut has been put on hold after the number eight tested positive for Covid-19 upon his arrival in Belfast.
The South African World Cup winner completed his move to the province this week, as he begins a two-season deal with the Irish side.
However, Ulster say he won't be available for this Saturday's trip to the Ospreys in the United Rugby Championship, having returned a positive Covid-19 test.
Vermeulen had been set to feature for the Barbarians in their Test match with Samoa last Saturday at Twickenham, before the game was cancelled just hours before kick-off following a Covid outbreak in the Baa Baa's camp.
"As a result of testing positive for Covid-19 prior to entering the professional squad bubble, Vermeulen will not train with the team this week," Ulster Rugby said in a statement.
"He will continue to be monitored medically and is currently well.
"The Public Health Agency has been contacted, and it is expected that he will integrate into the squad over the course of next week."
The province hope to integrate the 35-year-old forward into training next week, meaning he could potentially be available for their meeting with Clermont Auvergne in the Heineken Champions Cup on 11 December.