"I gave him confidence and he has himself recognised that it was good for his development to play another year at Everton. There is a very good contact and appreciation between us," Koeman told Belgian newspaper HLN.
"No one knows what will come after this season. If Romelu was to play at Everton until the end of his career, I know he has left something (behind). His potential is greater and higher than Everton, as a final destination."
Koeman compared Lukaku, who has scored seven of Everton's 15 Premier League goals this season, with clinical Dutch striker Patrick Kluivert and said the Belgian international had the potential to play for Spanish champions Barcelona.
News that makes sense
Your trusted source for staying up-to-date with the world around you. Get free daily news updates and analysis, straight to your inbox.
"Kluivert was also a striker who was quite young in the picture and had a fantastic career. Eventually Kluivert played for Barcelona, which could happen with Lukaku," Koeman, a former Barcelona defender, added.
"He is potentially a great striker, one who is only 23 years old. I think Lukaku is quite complete. He can hold a ball and be a target man and, because he is tall and physically strong. You can play directly with the long ball."
(Reporting by Shravanth Vijayakumar in Bengaluru; Editing by John O'Brien)
