I can see quite a few on here are writing off Lukaku, and I can see all the reasons why. He is our most costly striker. The main target man upfront. When he first came he was lean and hungry, scoring goals for fun, a shadow of the player he is now.
What happened? I would put the blame firmly at Mourinho's door. He left Lukaku up front on his own with no service from midfield or from the wings. We set up defensively, and rarely crossed the halfway line en mass, this left him playing with his back to goal and out-marked by multiple defenders. Before long he became a dejected figure, trudging about in a hopeless pursuit. He lost his edge, his match sharpness, and eventually his conditioning. Everyone said he needed a rest after the World Cup, and Jose was the last to acknowledge this.
If I was involved in the coaching staff, I would take him out of the squad for a few weeks, maybe send him over to the states for some intense conditioning training, working on his speed and losing a few pounds in the process. Then I would go back and look at the tapes of all the goals he scored and work out what makes him excel. What does he thrive on. Is it playing off the shoulder of defenders, and running onto balls over the top? Is it running into the box and heading in crosses? Or is it running onto through balls? We know what it isn't, and that is playing with his back to goal as the lone striker.
Next, I would have training sessions dedicated to employing all the methods that Lukaku thrives on. We know the midfielders can provide this, because it worked a treat when he first joined us. Pogba was picking him out for fun. If we all agree that Rashford is currently our main man and we have set the team up to play to his strengths, with the high press, one touch quick passing moves and catching teams on the counter, then we also need to prepare a plan B which incorporates the best of Lukaku, maybe even with Sanchez as a number 10.
It can work, we once had four very good strikers in our squad with very different strengths and weaknesses.