Petrovic was a standout last weekend at West Ham after Mandas and Forster joined the club in January to bolster the goalkeeping department.
Iraola praised the keeping trio and department, under the guidance of coaches Neil Moss and Gareth Stewart.
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On Petrovic’s recent performances, Iraola said: “I think he understands very well how this works, the Premier League, and I think he took like these signings like, okay, it's a challenge also for me.
“I need to step up. I think it has been positive. I think the atmosphere they have in the goalkeeping group right now probably is a more competitive one, but they are all good guys.
Djordje Petrovic. (Image: Richard Crease)
“They understand their situations. I hope they push Petro. He's playing now very well, but I hope they push him and they're making it very difficult until the end of the season because it's going to be very good for the team.”
Mandas joined Bournemouth on loan from Lazio in January and is yet to play a minute for the club.
Asked how he has dealt with his lack of minutes so far this season, Iraola praised the Greek stopper’s attitude.
“Christos trains very well,” he said.
“The more we see him training, the more confident I am with the signing. He stops a lot of balls. He's very agile, different kind of keeper. Comfortable on the ball.
Christos Mandas and Djordje Petrovic. (Image: Richard Crease)
“It's tough for me, and it's going to be tough, I think, until the end of the season. But it's going to be good for the team.”
On how much say he gets in goalkeeping decisions and how much he defers to the keeping coach team, Iraola said: “I don't get involved too much on the training methodology because I don't understand a lot about the things that they work on, or unless they explain.
“But I put all my confidence on them, and after I make the decisions, I take the decisions.
“Obviously what they think, how they see them training, is very important, but I am the one to blame. I am the one who has to take the decision. Always has been like this, and I think they understand it.”