Every club "would love to have a Romelu Lukaku in their squad", according to Everton boss Roberto Martinez.
Lukaku has scored 11 goals in his last 10 appearances in all competitions and has fully justified Martinez's decision to spend a club-record £28million to sign him from Chelsea in July 2014.
The Belgium international has voiced a desire to play in the Champions League - an ambition he may struggle to achieve at Goodison Park - but Martinez played a straight bat to questions on Lukaku's future ahead of the January transfer window.
He told a media conference on Wednesday: "Over the calendar year we can see he is in a really mature stage of his career. If you look at the way he works for the team, he has taken his game to the next level with the way he holds the ball up and brings other players into the game.
"He doesn't want to stand still. For such a young boy to have such a high level of consistent performance is important to us.
"We're under no illusions that everyone would love to have a Romelu Lukaku in their squad and that's why we made such a big investment in him."
The future of Lukaku's fellow forward Steven Naismith is less clear, however, with reports Norwich City have revived their interest in the Scotland international.
Martinez added: "We all know there was one Premier League club showing interest in Steven in the previous window, that's an open secret. There's nothing to comment on [now].
"During January we know how we need to need to move forward. We need to make sure we go through the window in the best possible way."
Everton were beaten 4-3 by Stoke City on Monday and Martinez is hoping captain Phil Jagielka's impending return can help cure their defensive frailty.
"We are in a period of the season where we feel we need to improve in certain areas," he continued.
"We want to be perfect. Defensively we are conceding too many goals for our liking. But there are reasons for that. This month is going to be very important as we will have our captain coming back into the side. We have a back four with a lot of talent but you need a bit of experience.
"We know as a team we are not far away from being a really strong team because our performances in between the boxes have been really impressive but defensively we've put ourselves in difficult positions to get the scorelines to reflect our performances.
"Winning games is what we need now. We've had too many draws. It's part of our learning curve to get as many points as we can."
