The 30 man squad includes Ulster new comer Grant Webb who has been signed as back row cover. Webb will provide much needed cover in the back row following injuries to two of Ulster's biggest hitters, Roger Wilson and Stephen Ferris who are both expected to return to rugby in 4-6 weeks.
Webb was speaking to www.ulsterrugby.com earlier in the week and was pleased to be in Belfast.
"I had been looking to move into Europe for quite some time so when the opportunity presented itself it was an easy decision, I've hit the ground running as I started training the morning after I arrived, everyone has been very welcoming- Paul Steinmtez has been showing me around."
Also included in the extended squad is David Humphreys who has been struggling with an ankle injury since September.
Williams will name his final team at noon on Sunday.
ULSTER RUGBY SQUAD TO PLAY LEINSTER
Backs
M Bartholomeusz; S Danielli, B Cunningham, M McCrea, T Bowe, A Trimble, R Dewey, P Steinmetz, N O'Connor, P Wallace, D Humphreys, P Marshall, I Boss, K Campbell
Forwards
J Fitzpatrick; B Young, D Fitzpatrick, T Court, R Best, N Brady, S Philpott, J Harrison, R Caldwell, C Del Fava, M McCullough, N Best, K Dawson, D Pollock, C Henry, G Webb
Guinness PRO12
Suite 208, Alexandra House,
The Sweepstakes
Ballsbridge, Dublin 4, Ireland