Midfielders David Havili and Jack Goodhue as well as the coaches are in isolation after contracting the virus and have been kept away from the team in Auckland.
Their Crusaders teammate Braydon Ennor has been called in as a replacement.
Foster said that they were prepared for the scenario and he was confident all would go to plan for the Eden Park clash.
"We've had a plan for this happening, and it's a great opportunity for the wider coaching group and the senior players, who will be highly motivated to step up," Foster said in a statement.
"We have learned how to cope with the unexpected, like everyone has over the past couple of years.
"I will still be working alongside the coaches and team via Zoom and I have huge faith in the coaching group and the players.
"We have structures in place and everyone is working together."
With Foster and Plumtree also in seven days isolation, assistant coaches Brad Mooar and Scott McLeod, alongside scrum coach Greg Feek, will take over.
Havili was expected to start at inside centre with Blues' ace Quinn Tupaea his likely replacement.
Ex NRL star Roger Tuivasa-Sheck could now be in line for a spot on the bench, which may see him make his Test debut.
