The former Arsenal midfielder, 23, has made no secret of his desire to quit the club and return south for family reasons.
But Benitez says: "When he wanted to go you could see he was not happy and, at the beginning, it was not easy.
"But when he started playing games, and playing well, you can see his face every day - he's enjoying himself.
"It's something that he will analyse at the end of the season. Maybe he will stay. We have to wait. If he's playing well and is happy, you never know.
"The main thing for anyone in your job is to do well.
"But I think he can play even better, progress and be in the national team. He has the potential to play for England."
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