Young back rower Thomas Anderson (knee) the latest to join the list, leaving Williams particularly in the second row and back row with Carol Del Fava and Ryan Caldwell also unavailable at present.
Williams, however, was philosophical about the province's injury situation, saying: "We've been unlucky in that we've had a number of longer term injuries this season and our match against Llanelli away in the Heineken Cup was particularly bruising, but it happens to everyone and it's just our turn."
Ulster captain Rory Best has been rested this week and in his absence experienced flanker Kieron Dawson will lead the team.
"If we go down to Munster, tackle our hearts out and stay within 10 points then we have every chance," Williams added.
"We're playing the leaders but this is a really healthy competition. Everyone is alive and fighting.
"The top teams beat the bottom teams and the bottom teams beat the top teams, it's a very close and competitive league."
The finalised Ulster team and replacement will be announced on Friday.
ULSTER Squad (v Munster): Backs (12) - Isaac Boss, Darren Cave, Bryn Cunningham, Ian Humphreys, Paul Marshall, Mark McCrea, Timoci Nagusa, Niall O'Connor, Clinton Schifcoske, Paul Steinmetz, Andrew Trimble, Paddy Wallace.
Forwards (13) - BJ Botha, Nigel Brady, Tom Court, Kieron Dawson (capt), Robbie Diack, Stephen Ferris, Justin Fitzpatrick, Chris Henry, Matt McCullough, Ed O'Donoghue, Filo Paulo, Stuart Philpott, David Pollock.