Ferguson watched his Championship strugglers fail to win for the 13th time in 18 games at London Road on Tuesday, although they were grateful for a point as Michael Bostwick's 71st-minute equaliser rescued a 2-2 draw.
A disappointing midweek result leaves the Posh two points adrift of safety and lacking in momentum at the start of a potentially crucial week.
Ferguson said: "In our situation any match we fail to win goes down as a missed opportunity - that's certainly the case tonight.
"We failed to take some fantastic chances to get a second goal after going in front and then we were all over the place after Charlton came back at us.
"We got ourselves together again to equalise and could have nicked a win at the end, but our home form hasn't been anywhere near the level we expect all season and that is clearly an issue we need to address.
"I viewed this week, with Charlton at home tonight and Ipswich coming here on Saturday, as a great chance to put six points on the board.
"The most we can get now is four and that makes Saturday the biggest game of our season. It is a must-win if we are serious about staying up."