Thirty-three-year-old Saha spent four years at Old Trafford between 2004 and 2008, netting 42 times in 124 appearances, before moving to Premier League rivals Everton.
The recently-recalled France international joined Spurs on transfer deadline day in January and has made a blistering start to life at White Hart Lane, scoring three goals in three games.
Saha will be keen to continue his prolific start for the North Londoners against his former employers, and veteran tactician Ferguson admits he will prove to be a handful.
"I don't know the circumstances behind Louis Saha's transfer but Everton were happy to let him go," he told Inside United.
"And then he goes to Spurs and scores two goals [against Newcastle United]. That's typical of Louis. He's got tremendous talent, he just doesn't play enough.
"He is a handful, no doubt about that. He's got two great feet, he's quick, he's got a good spring in the air. There's no doubt he is a handful."
Spurs head into the fixture eight points behind United and 10 adrift of league leaders Manchester City after last weekend’s 5-2 defeat to rivals Arsenal.
And the Scot concedes his side will have to be on top form if they are to take anything away from London on Sunday.
"They've got a fantastic squad, and a goal threat throughout the team," he added.
"Gareth Bale contributes, Rafael van der Vaart, [Jermain] Defoe, [Emmanuel] Adebayor. They've got goals in their team."
