Ulster back row Marcell Coetzee is to have surgery next week after sustaining a serious knee injury.
South African star Coetzee was injured in Saturday's Pro12 win over Zebre.
The 25-year-old had only recently resumed playing after a long injury lay-off, making his Ulster debut against Edinburgh last month.
It is believed Coetzee has hurt the same knee and will have exploratory surgery to find out how serious the latest injury is.
The loss of Coetzee for another lengthy spell is a huge blow to Ulster and their director of rugby Les Kiss.
When the player was declared fit to make his Ulster debut against Edinburgh on 10 February, Kiss said: "It's like a new signing.
"I think we will see some good things, but we will see better things the more he plays."
Former Natal Sharks player Coetzee joined Ulster on a three-year deal at the start of the 2016/17 season.
In another injury update, Ulster reported experienced winger Andrew Trimble had undergone surgery for a left hand fracture sustained in the home win over Treviso.
The 32-year-old is expected to return to action in around four weeks.