Ulster and Ireland utility back Will Addison has been ruled out for the remainder of this season after undergoing a back operation.
The 26-year-old, who joined Ulster from Sale last summer, has not played since January because of his back injury.
The former England Under-20 player made his Ireland debut last November.
Ulster centre Stuart McCloskey is a doubt for Friday's crucial Pro14 game against Edinburgh after being concussed in last weekend's defeat by Glasgow.
An Ulster statement said that McCloskey, who has earned three Ireland caps, would follow the return to play protocols.
The statement added that Ulster are hopeful Addison will "return to full fitness for pre-season".
Last Friday's 30-7 defeat by Glasgow has heaped pressure on Dan McFarland's Ulster side heading into Friday's game at Murrayfield.
With two rounds of fixtures left in the regular season, Ulster are second in the Conference B but both Benetton and Edinburgh are within three points of the Irish province.
An Edinburgh victory on Friday could see Ulster dropping out of the three play-off places if Benetton defeat Munster in Treviso on the same evening.
In the final round of fixtures on 27 April, Benetton, now two points behind Ulster following their draw with Leinster in Dublin last weekend, will be fancied to take full points when they face Zebre away.
Ulster's final fixture sees them facing Leinster at Kingspan Stadium in a repeat of the recent European Champions Cup quarter-final which the holders won narrowly.