O'Neill told Villa's website: "He has done brilliantly since his arrival at the club, really brilliantly. I am absolutely thrilled for him.
"I remember reading after he signed for Villa that one of the reasons he joined was because Fabio Capello came to see a lot of Villa games - I remember thinking 'I hope that isn't the only reason you joined the club'.
"I am just really, really pleased for him. He has done exceptionally well and fitted in brilliantly. In fact, I wouldn't be surprised if he was a little shocked himself at how quickly he fitted in after that debut against Birmingham City.
"He is just so solid and reliable. He is brave, he puts his head in - he's just a really exceptional player.
"I still think he can keep improving.
"I always thought he was a really good player but it's only when I started working with him on the training ground that I realised he's even better than I thought. I really think he can improve further too."