Postponed from its planned 2025 French staging, the World Cup moved to co-hosts Australia, New Zealand and Papua New Guinea; the field fell from 16 teams to 10.
England are in Group B with Lebanon and Samoa, but play Group C's Tonga, Papua New Guinea and France.
Two teams from Groups B and C combined advance, alongside Group A's top two; Group A has four teams.
Tonga's win was its first-ever against England, and its side had more NRL-based players.
"The jeopardy of losing one game in a pool of three is so harsh, it's almost like we don't get another chance to straighten things out," McDermott told the media ahead of France.
He added, "There's still a slim chance that we get through, and that's something we're focusing on, we remain determined."
He also said, "The jeopardy is really harsh and we knew for us to go through that we had to go and beat Tonga."