McGrath is seeking almost $US400, 000 from the SRU and its CEO Faleomavaega Vincent Fepuleai for wrongful dismissal and alleged defamation of character.
He was sacked in September after Samoa failed to qualify for the Rio Olympics.
SRU Chair, Prime Minister Tuilaepa Sa'ilele Malielegaoi, told Samoan media last week that McGrath was acting like a cry baby.
The now Canada sevens coach said the Prime Minister's comments were nothing he didn't expect.
