The Kop boss said: "We knew he had power, pace and movement which would suit the Premier League. He's scoring goals, playing well and his understanding with the others is good.
"We already realised how strong he was and he will be even stronger in a few months. He's working really hard. When you talk of strikers, you can have someone who gets 20 goals a season but is just waiting for chances. If you have someone who gets 15 but creates 10 or 15 for the others, it's better."