Matthew Mott says that England's Twenty20 loss to South Africa is a line in the sand for the team.
In the third T20 at the Ageas Bowl, the hosts were defeated by 90 runs.
England have not won a white-ball series at home this summer and have lost three consecutive T20 series.
Mott said that they were down on confidence.
I was disappointed. I think we have a good chance to win the series and we will take a lot out of that game.
The former Australia women's coach was appointed in May, with Buttler taking over as limited-overs captain from Morgan after he retired from international cricket.
"This is a line in the sand moment for the team and I spoke to him briefly," said Mott.
England's white-ball batting has been poor this summer, with four of their six T20s against India and South Africa being washed out.
They have just 10 games left until the T20 World Cup starts in Australia, followed by a seven-game series in Pakistan in September.
The upcoming Hundred will give players a chance to get some confidence.
When we get ready for Pakistan and the World Cup, we're a bit of a different team because we'll want to draw some experience from The Hundred.
After beating South Africa by 41 runs in the first T20, England were dismissed for 149 to lose the second match by 58 runs and were then whitewashed by 101 in the decider.
"We came in with high hopes to win the series and we never really got going," he said.
"They were a bit over par with the bat, and we just lost too many of them to mount a challenge at the end." On the last day, it had a sour taste.
England hit a world record 498 in the first one-day international against the Netherlands.
They failed to win a white-ball series during a home summer for the first time in four years after losing both the T20 and one-day series to India.
It's been a bit of a challenge. Throughout the summer, we had ups and downs.
We played two great teams and came out second.
In the last 25 days, England have played 12 white-ball games, but Mott didn't want to make excuses.
The quick changes haven't helped but we need to be better than that.
"We have to acknowledge that we're still professional cricketers and you have to go out and front up and that performance was not what we want to be renowned for."