Ferguson has repeatedly expressed concern about Manchester United's defending this season.
In the wake of their 4-3 defeat at Reading last Saturday, the United boss said if his team did not improve `God knows what will happen' at the Etihad Stadium on Sunday.
The Red Devils subsequently went behind for the 15th time in all competitions this season as they lost Wednesday's Champions League encounter with CFR Cluj.
And, with Ferguson claiming skipper Nemanja Vidic will not be returning to first-team duties on Sunday as he hoped, it is down to Rio Ferdinand and company to try to restore some much-needed stability.
"It's not as if we're ignoring it," said the United boss. City will have expected us to have been working on it.
"Nicky Shorey's delivery was brilliant last week and that put us under pressure. But we have the players to handle that and we should be doing better."
The concern is heightened because City won the corresponding fixture last season thanks to a Vincent Kompany header in first-half stoppage time scored in much the same way as United have conceded so regularly this term.
"I am sure City will be working on set pieces because I think we've lost something like 10 goals from set plays this year, which is a lot," said Ferguson.
"We're hoping to find a solution and we're hoping a solution makes a difference."