Newcastle confirmed on Sunday morning that they were working through the matter in conjunction with the NRL.
Knights chairman Brian McGuigan said the club respected McManus' right to sue, but would be defending its handling of his concussions.
"Players have got to be approved to go back on the ground by the doctors, the medical staff," McGuigan told Fairfax Media.
"If he is deemed to be fit, all we do is abide by that, all we have ever done is abide by that.
"We have never put anyone under pressure to go back on the field were they not approved by the medical staff as being ready to go back on the field."
McGuigan also said the legal action would have no impact on McManus' current position at the NRL club.   The NRL is not commenting on the matter.
- AAP