The former England defender, who will be 34 when United take on Braga, has been working overtime this season.
Fergie said: "The game in Braga will give me a chance to utilise my squad. I'll be making some changes.
"If we can get the win it's better, but we want to make sure we qualify first. If we do, it gives me options to utilise Smalling and Jones.
"Then we can make sure that Ferdinand is fresh for all these games. I won't have to worry about playing him Saturday, Wednesday, Saturday, Wednesday.
"That's an important issue. I don't expect Vidic to be back until Christmas so it adds back-up in that respect."