Lang said he hoped the pair would be fit for the February 14 match.
"You'd have to say they'd be in some doubt," Lang said.
Ryan Girdler tore his calf muscle in Penrith's grand final win last October and aggravated it on the Kangaroo tour.
Campbell is battling a groin adductor injury suffered in the pre-season.
"Girds hasn't run flat out yet, but he should be right," Lang said.
"It's gradually building up and we're being pretty conservative with it.
"If you had asked me last week about Preston I would have said he was less than 50-50, but he's been coming good over the last week."
Penrith announced a team for the World Sevens missing all their first graders in order to keep them fit for the World Club Challenge.
Lang said had first graders been considered for the sevens, Girdler and Campbell would not have been selected anyway.