Hiddink told Russian newspaper Sport Express: "I think he still needs to improve - all the more because the other day I read Harry Redknapp had said it would be better if Roman spoke in English.
"But with Arshavin we have spoken a few times on the phone and I would say that his colloquial English is already perfect. On the phone you can only count on your vocabulary - gesturing is no good - and Arshavin copes with this perfectly.
"Generally, Arshavin can't be stopped, he is proactive and always wants to improve. Pavlo is a little different. He knows that I like him very much, but I always say to Roman that he should not succumb to his inherent tendencies of complacency.
"At Euro 2008 - and when we were preparing for the European Championship - he was as sharp as a dagger. In these matches he won universal respect. If he wants to be successful in his career, he must maintain this approach."