Iraola says the former Chelsea goalkeeper has improved thanks to competition from Fraser Forster and Christos Mandas.
"I have spoken before about how important players who don’t play can be sometimes and, in this case, it’s very clear," said Iraola.
“Fraser Forster has been so beneficial for Petro because he has played a lot in the Premier League, he has a lot of experience and he has been there. I think he trusts Petro a lot and I think you can feel it, even in training.
“In a different way, Christos has put this competitive edge on him. He trains very well and to a very high level.
“But Petro is not giving me chances to change him. This competition is very good for the team and, like everyone else, I think Petro has improved as the season has progressed.
“Overall, the team is doing better so everyone looks better. We probably don’t notice the mistakes because we are doing very well so everything looks better.
“I’m happy because I think the movements we did in the goalkeeping department in the winter market have been beneficial for everyone, I would say.”