Denis Betts believes confidence at Widnes will be affected by Saturday's last-gasp defeat to London Broncos.
Antonio Kaufusi's late try was enough to the lift the Broncos off the foot of the table, with Widnes replacing them.
Vikings coach Betts told BBC Radio Merseyside. "That win could have massively changed our whole season.
"In essence now, we're just still doing the same things. We're working hard to drag ourselves off the bottom of the table every week."
A week previously, Widnes had snatched a late victory against a faltering Huddersfield side, but they were on the wrong end of a late score in a clash between Super League's bottom two teams.
"It's a bitter pill to swallow because we lost at the death, but we won one like that last week," added Betts.
"They worked really hard and, to lose it like that, the swing in confidence is massive from that one play. It changes it completely."
Betts also revealed that some of his players had been suffering with illness in the build-up to the 28-24 loss.