Manchester United have three players - England duo Chris Smalling and Tom Cleverley, plus skipper Nemanja Vidic - who have a chance of being fit for the crucial Premier League visit to Liverpool on October 15.
"The most important thing is the work they do before the internationals finish," Ferguson told MUTV.
"We really want to have Vidic and Cleverley doing some really strong work, and Smalling too, that would bring them on to a level that they could play at Anfield.
"You can't go there with players who are semi-fit or just coming back from injury. You need players who are fully focused and up to speed in terms of fitness and sharpness."