Williams - who has settled in at left-back for the Royals since his summer move from Scunthorpe - spent the early part of his career at the City Ground and knows Forest will be a tough proposition.
He said: "I was there many years ago. I was there from the age of 11 to 14 after a couple of lads from my Sunday team got signed up. "I was playing as a left winger then and was in the team with James Perch who has just gone to Newcastle. "They were a big club then and they still are now. It will be a tough game."