Manchester United captain Nemanja Vidic will not make his return from injury in the final Champions League group game at home to Cluj.
Vidic, 31, has not played since knee surgery in September but had been lined up to feature against the Romanians.
But the defender has now been ruled out, and will also be unavailable for Sunday's Manchester derby.
Wayne Rooney will start in a much-changed side, as United have already qualified as winners of Group H.
Ferguson said: "I do not think Vidic will play. He feels he needs another few days' training.
"He will not play in the derby if he doesn't play tomorrow, although I wasn't considering him for Sunday anyway.
"We'll rest some players but we have to be fair to all the teams who are trying to reach important positions - whether that's the Champions League or the Europa League.
"In that respect, we'll play a team that we expect will win. But there will be changes."
Ferguson also confirmed Japan international Shinji Kagawa has returned to training after his knee injury and there is an outside chance he could be involved at the weekend.
Provisional squad: Lindegaard, De Gea, Rafael, Jones, Smalling, Wootton, Ferdinand, Buttner, Evra, Cleverley, Giggs, Fletcher, Powell, Scholes, Carrick, Young, Hernandez, Welbeck, Rooney, Van Persie.