"People have been very critical of him and tried to compare him with other players of the past. But if you were to see the price of the player and compare that with other players then you would know the criticism has been very unjust," said Benitez.
"Antonio is not at his level yet, he knows that and we know that, but we didn't pay a penny for him. Okay, he's not playing well but he is working very hard to improve and that is the most important thing.
"It has been very difficult for him. If you arrive at a new club in a new country from Real Madrid then you are under pressure.
"Then if you get injured on your first day and are out for three months and then come back into an inconsistent team it is very difficult.
"I know he is not playing well but I don't think it is fair to judge him with other players from the past and not to give him the opportunity to improve. He will improve. He has a good mentality and will give 100% for the team."