First-choice midfielder Hopper (knee) and premiership defender Broad (calf soreness) were named in the initial extended squad for Sunday's clash with the Power at the MCG, but have since been withdrawn.
They join Josh Gibcus (knee), Dion Prestia (hamstring) and Tylar Young (concussion) on the sidelines.
Ben Miller, James Trezise, Tom Brown and Sam Banks have been called up alongside Lefau.
The Tigers' inclusions boast just 34 games' experience between them - 25 of them from Miller.
New Zealand-born Lefau will line up in his first senior game just over a month after he was handed a spot on the Tigers' rookie list.
Lefau crossed the Tasman in 2012 and has since made another move - from rugby league to AFL. (James Ross/AAP PHOTOS)
The 195cm, 96kg prospect made his presence felt during the pre-season with a brutal bump on Melbourne's Jake Lever in a practice match, and caught the eye with a clever goal.
Lefau's rise through AFL ranks comes after he spent time in NRL club Melbourne Storm's development pathway, following his move to Australia from Auckland in 2012.
"All the boys know what I can do in that (physical) sense, so I just try to bring that to the best of my ability because I know I can do it," Lefau said last month.
"If anyone's there I'll put my body on the line for the boys.
"The toughness maybe (is from my rugby league background), but there's all that technical stuff as well.
"You've got to be smart with it and that was a big learning curve for me, trying to get my body in the right position, because you don't want to injure someone or get in trouble."
Warm favourites Port Adelaide have also suffered injury blows, losing prime mover Jason Horne-Francis (hamstring) and Jed McEntee (concussion), who have been replaced by Jase Burgoyne and Dylan Williams.
West Coast have named ruckman Harry Barnett to debut in their clash with GWS at Optus Stadium on Sunday, with Jamaine Jones and Ryan Maric also called up.
They replace injured captain Oscar Allen (knee) and dropped pair Andrew Gaff and Alex Witherden, while the Giants recalled James Peatling in place of Nick Haynes (personal reasons).
The Western Bulldogs made a big call for their meeting with Gold Coast in Ballarat, dropping Rory Lobb for young gun Sam Darcy.
Oskar Baker and Caleb Poulter are also in, with Lachlan McNeil dropped and James Harmes suspended.
Gold Coast's Jed Walter will debut, while co-captain Jarrod Witts (injured) and Malcolm Rosas Jnr (suspended) are unavailable.
