Brisbane skipper Darius Boyd is set to return from two weeks sidelined with a hamstring injury.
Slater said his inclusion was massive for the Broncos.
"They won last week when they had injuries so they will gain a lot of confidence out of that and, if they get Darius back, it's a huge boost for them," Slater said.
"He's a tremendous player and probably the most-important player in their team, certainly structurally in defence."
Halfback Cooper Cronk is also still to make a call on his playing future but the grand-final qualifier will definitely be his last with the Storm in Melbourne after announcing mid-season his plans to move to Sydney.
Forwards Jordan McLean and Tohu Harris are also leaving Melbourne for other NRL clubs.
Slater said it was important to send those players out on a winning note but it wasn't the main motivation.
"There's a lot at stake this weekend, and sending them out from AAMI Park on a good note is important to us but we've worked really hard for the last 11 months and we're now 80 minutes and a good performance away from a grand final."