A 39-19 loss to the Otago Highlanders in Auckland on Friday night delivered another hammer blow to Moana's hopes of reaching the play-offs for the first time in their five-season existence.
The visitors were 32-0 ahead early in the second half before Umaga's side launched a late response with three tries.
However, it couldn't halt a miserable run of heavy losses for Moana since winning their opening-round match against Fijian Drua.
Umaga admitted he had a less experienced core of players at his disposal than last year, when All Blacks great Ardie Savea was an inspirational figure.
Savea led Moana to their best record of six wins to narrowly miss the play-offs.
His departure this year for Japan, along with the absence of several other important players had weakened Moana's know-how, Umaga said after the match on Friday.
"The players that are here, they're learning what it takes to be a professional rugby player and it's more than just playing and training," he said, referring to aspects such as diet and sleep.
"You still have to be professional in all those things.
"And this tournament's tough. I don't think people realise the attrition rate and the need to back up week after week."
It is the last season in charge for former New Zealand captain Umaga, who this week was named among the group of assistant coaches to work alongside new All Blacks head coach Dave Rennie.
Umaga said he won't lose sight of his role with Moana, the team comprising players of Pacific heritage.
The Highlanders dominated most of the contest to pick up a third win.
However, coach Jamie Joseph believed they lost their rhythm after a power outage at North Harbour Stadium halted play.
The last 20 minutes were played without television match official oversight and were not broadcast.