Lukaku has been linked with a return to former club Chelsea this summer after bagging 25 Premier League goals for Everton last season.
The Belgian striker refused offers of a new contract and could be on his way out the door this transfer window, but who will boss Koeman bring in as a replacement?
Recent reports suggest Wayne Rooney is set for a shock return to Goodison Park, while Arsenal frontman Olivier Giroud may also be looking for a new club with Alexandre Lacazette moving to the Emirates.
Ex-Barcelona youngster Sandro has already arrived this summer but further reinforcements will be needed if Lukaku does move on.
Source: Daily Express