The Manly Sea Eagles are set to be without a key back-line player for an extended stint, which will see a youngster re-enter the starting team.

After playing all 80 minutes against the North Queensland Cowboys on Saturday, it has been revealed by The Daily Telegraph that Tolutau Koula has sustained an MCL injury.

The injury to Koula - who shifted to the No.1 jersey last round - will see him miss around a month of action as the competition enters the backend of the season.

Koula's absence will see Lehi Hopoate re-take the fullback position with coach Anthony Seibold intending to keep Tom Trbojevic in the centres, per the publication.

The son of former NRL player John Hopoate, Lehi has made five appearances this season, four of them in the number one jersey.

During his time on the field he has scored one try, created two try assists, made 15 tackles busts and is averaging 128 running metres per match.

The club will also be without second-rower Ben Trbojevic for next week's clash against the Newcastle Knights after he failed a HIA on Saturday and has entered the NRL's concussion protocols - the 11-day stand-down period.

Captain Daly Cherry-Evans and Jake Trbojevic will also be absent due to Origin responsibilities but Haumole Olakau'atu will remain in the side after being dropped from the NSW Blues team by Michael Maguire.