"He's certainly raring to go," Foster said.
"He's done his four-game suspension. It's been an awkward time for him, it's been tough.
"But he's made sure that he has used that time smartly, he's trained well and been able to get on top of a couple of niggles.
"He's back charging around, you've got to sort of hold him back a little bit."
That won't be the case on the weekend, when Williams is set to tackle the Wallabies.
Williams knows ANZ Stadium well, having won NRL premierships with both Sydney Roosters and Canterbury Bulldogs.
"He said he didn't have the money to live in Double Bay so I don't think he knows this part of Sydney very well," Foster laughed, when asked about Williams' intel.
"He's clearly lived in Sydney before, but really his eyes are on one task and that's us doing well on Saturday.
"He's doing everything he can for this team to make sure we prepare well."
All Blacks playmaker Beauden Barrett was full of praise for Williams' attitude during his suspension.
"He's as positive as ever," Barrett said.
"Even throughout the Lions series we saw that of Sonny, he got over it pretty quickly."
- AAP