Ulster lock Alan O'Connor has been ruled out of Friday's Champions Cup clash with the Scarlets at Kingspan Stadium.
The second row picked up an ankle injury in the win over the Cardiff Blues and missed last weekend's victory at the Scarlets in the first of their European doubleheader.
It was hoped he would be back for this week's return fixture, however it has been confirmed he won't make the matchday squad.
That leaves Ulster short of locks again, with only Iain Henderson and Kieran Treadwell available in the European squad and back row Matty Rea covering on the bench.
Ian Nagle could return this weekend having also missed last Friday's game in Llanelli, however he is still a big doubt to be involved.
Flanker Sean Reidy is also a doubt having been taken off for an HIA in the game at Parc y Scarlets, while winger Craig Gilroy continues to be sidelined.