Manu, 34, has a dislocated and broken thumb and will miss the next six to eight weeks, while Laffranchi will be out for a month with an arm injury.
Both suffered knocks in the 30-28 win over Castleford last Friday, and their absence is a blow to Nathan Brown ahead of the Good Friday derby clash with Wigan.
He said: “Friday’s game wasn’t kind to us but we’ll be fine.
“We’re looking forward to the match and it will be a great contest. Wigan are a terrific team and what they achieved last year was big considering how tough a double is to do in the modern game.
“There is a respect between the clubs, the intensity rises and it is a big clash for both communities. The friendly game showed that too.”