The 21-year old New Zealand international, on loan from West Bromwich Albion, has netted eight goals in the Championship so far this term and the Seagulls could very well make a move for him inside the January transfer window.
"We had him here when he was very young (in 2010) and we helped each other. He helped us a lot with his power and his goals," Poyet told the Argus.
"I think we did our job as well to put him in shape, because he was still growing up.
"I think he is a much better player now. He is mature, he has learnt a lot about the game in England. He is playing week in week out, so he's much better.
"There has been plenty of talk and he is a player we know very well, which would make it very easy to make a decision one way or the other.
"At the moment he is with Millwall, so I don't want to make a mess before the game just in case they take it the wrong way, so we'll see."