Williams has recovered from a groin injury and is expected to replace utility man Charlie Lee.
Ferguson may include winger Chris Whelpdale, who missed the start of the season following a hernia operation, but Jamie Day (ankle) will not feature as Posh aim to avoid a third successive league defeat for the first time since January 2007.
Midfielder Lee Frecklington could make the 100th league start of his career after scoring against Ipswich in the Carling Cup on Tuesday.
"Every footballer wants to play week-in, week-out, but that's not always going to be the case," the 23-year-old told BBC Radio Cambridgeshire. "I did alright against Ipswich so hopefully I'll get another game on Monday against Palace."
Meanwhile, Posh youngster Sam Gaughran has joined Grays Athletic on an initial one-month loan deal.
Kick-off at London Road is 5:15pm.