Liverpool were held to a goalless draw at home by winless Fulham on Saturday, their third dropped points in four Premier League matches this season.
The result came less than 72 hours after Liverpool had come from behind to beat Atletico Madrid 2-1 at Anfield in their opening Champions League group game.
Iraola made three changes to his starting line-up for the visit of Fulham, but his side lacked energy and cutting edge throughout, managing only their fifth goalless home league game in almost eight years.
Alisson did not shy away from a blunt assessment afterwards.
"It was a poor performance, in some moments even from myself, but from the team," said Alisson. "Collectively, we didn't play well. Many things we tried to do, we couldn't do it well. We couldn't press them well.
"In the first half we spent too much energy trying to press them in a good way, but we couldn't."
The Brazil international pointed to the toll of a packed early-season fixture list, with another quick turnaround to come.
"Obviously, it's a big challenge to play Wednesday night and Saturday evening, and you have another game Tuesday," he said. "But we need to get the right mentality to do that and I think it wasn't the case.
"Deep inside we have it, we just need to put it out. The quality we have, we have so many top players, but we need to take and put more energy on the pitch for the next games. We have to improve for the next one."
Liverpool return to action on Tuesday when they host struggling Tottenham Hotspur in the Carabao Cup, a fixture Iraola may use to freshen up his selection.
Alisson warned that Liverpool's season will amount to little if they cannot adjust quickly to the demands of competing on multiple fronts.
"It takes it out, but we recovered the best way we could," he said, reflecting on the energy spent against Atletico Madrid. "This is the challenge for every big team who are playing in all competitions.
"If we want to do something special this season we have to cope with that: to play a big game on Wednesday night, another one on Saturday, then next Tuesday you have another one, then on Sunday again. It's what we want."
The goalkeeper also acknowledged the adjustment period that comes with a managerial change, with Iraola only recently installed at Anfield.
"It's not easy," he said. "That's another thing as well that is a challenge - when you change manager. But he is doing really well, he is helping us in so many ways.
"His staff as well are helping everyone; we have a good environment as well, a good atmosphere in the training ground. Everybody is excited about the new signings as well, about the quality we have in our squad.
"It can take some time for us to adapt to that, but we need to do that as quick as we can because we don't have time to waste."
Liverpool remain unbeaten in the league this season, but Alisson made clear that stretching a run of draws holds little value.
"We are not happy at all with a draw," he added. "Unbeaten with three draws is not something to celebrate too much with this shirt - we celebrate being unbeaten if we win the games."