The Belgium international is currently on a season-long loan deal from Chelsea, and currently tops the Blues' scoring charts with five goals.
"As you can imagine I have never been a centre-half in my life and when I see centre-forwards like Romelu Lukaku I am glad about it!" Osman told the Daily Mail.
"He has got everything and he is going to be a top, top centre-forward. It was a masterstroke by the gaffer (Roberto Martinez) to get him and the frightening thing is that he is only going to get better.
"In fact, I'd go as far to say that he is already under consideration for my Fantasy Football team. And there is no bigger accolade than that."
Lukaku spent last season on loan with West Bromwich Albion, finishing as their top scorer with 17 goals.