As of Wednesday evening, the two were also missing from the club's list 30 of players on their official team website.
Matai and Stewart, who have scored 254 tries between them in 462 games, are yet to return to proper training just a month out from the club's opening-round clash with Parramatta.
It has allowed the club to prepare as if the duo won't be there this season.
Tom Trbojevic will slot in at fullback for this weekend's trial against South Sydney and former Gold Coast junior Brian Kelly is partnering Dylan Walker in the centres.
Stewart or Matai are each signed to the end of the year, and the club - who are desperate to see them finish with the respect they believe they deserve - would need to show to the NRL that their injuries are not pre-existing prior to their re-signings to have their wages not counted in the season's salary cap.
Matai has not played for Manly since round nine last year, while Stewart missed the final 10 weeks of the 2016 season with his knee injury.