The jet-heeled wing will line-up for the Barbarians at the Millennium Stadium, in his final professional outing.
Wales caretaker coach Rob Howley has already warned Williams to expect an “aerial assault” and the two-time Grand Slam winner is braced for some special treatment.
“I’m sure they won’t let me off lightly and I wouldn’t expect anything different,” said Williams.
“Facing the guys is going to be difficult, but at the end of the day it’s an international game of rugby and I need to switch on.
“Yet I will need to make sure I don’t get dragged around by the big guys in the Wales team. We are friends off the field, but I’m not sure that will be the same on the field on Saturday.
“I need to go out there and play my own game and then I can celebrate with the guys afterwards.”
More than 50,000 tickets have already been sold for the clash where Wales will bid farewell to Williams and his namesake Martyn, who will win his 100th cap.
And, while the 2008 IRB World Player of the Year admits the away dressing room will be unfamiliar territory he insists it will be the perfect occasion to draw the curtain on his illustrious career.
“I’ll be playing at the Millennium Stadium where it all started for me, even though I’ll be in the away dressing room which I won’t obviously be used to, and I’ll have all my friends and family there,” said Williams.
“It will be great to play against Martyn and catch to up with him afterwards.
“He’s a true ambassador for the game. I’ve been trying to get him his 100th cap over the last couple of months because he deserves it.
“He is a player who has sweated blood over 15 years and deserves his moment, not just because he’s going to get 100 caps but because he’s a legend of Welsh rugby.”
The former British & Irish Lions Test wing will come up against Cardiff Blues rookie Harry Robinson, who has already been described as “Shane-esque” by Howley.
“I’m really pleased for him, he’s done well for the Blues this season and I’m sure we’ll see him play many more times for Wales,” added Williams
“He’s a fantastic little player, strong, gutsy, and that’s what I like in a player.
“Hopefully he won’t make my life too difficult on Saturday. Perhaps we’ll have a gentlemen’s agreement before the game to help each other over the line for a couple of tries!”
