Newcastle forward Robbie Rochow's NRL season is over due to a pectoral tendon injury, while his teammate utility Sione Mata'utia is out for four weeks due to a broken jaw.
Rochow and Mata'utia suffered the injuries in the Knights' round-19 loss to Melbourne at Hunter Stadium on Sunday.
The Knights confirmed the extent of the injuries in a statement on Monday.
"Robbie Rochow requires surgery to reattach his pectoral tendon following Sunday's match against the Melbourne Storm," the statement read.
"Rochow saw a specialist in Sydney on Monday afternoon after scans revealed a tendon injury on Monday morning.
"Rochow is scheduled for surgery on Tuesday, which is expected to sideline him for four months.
"In other injury news, Sione Mata'utia suffered a broken jaw in Sunday's loss. The injury is expected to keep him out for four weeks."
In good news for the last-placed Knights, Queensland winger Dane Gagai is expected to return from a quad injury against Cronulla on Sunday, after missing the clash with the Storm.