The Moroccan midfielder has established himself as a regular in Paul Lambert's starting XI and scored his second goal of the season in Monday night's derby draw at Albion.
"I think he still has a lot more to offer," said Vlaar. "We all want to see Karim playing well and he knows. He's working hard. I've known him for a long time now and he has a lot of qualities for sure.
"Of course it is always nice to know someone and that has helped us. It's easier to talk to him because we played in Holland for a long time. It was not easy for him all the time. Of course I have tried to help him as much as possible. He is definitely good enough to play in the Premier League."
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