Williams needs a strong performance in the Six Nations to convince British & Irish Lions coach Sir Clive Woodward he deserves a place in his squad for this summer's tour to New Zealand.
The Cardiff Blues flanker has been struggling with a disc problem in his neck but Wales team physiotherapist Mark Davies has delivered an encouraging fitness bulletin just five days before the eagerly-awaited Millennium Stadium showdown.
"We are pretty optimistic about Martyn," said Davies.
"He has made some good progress, and he will now have a few tests in the next 48 hours and we are pretty optimistic he is getting there.
"It has been a bit frustrating, but he is on the mend," Davies added.