Maurizio Sarri has labelled Eden Hazard "one of the best in Europe", but insists that the Chelsea forward can still step up another level.
Hazard is in contention to make his first start of the campaign on Saturday evening when the Blues play host to Arsenal at Stamford Bridge.
The Belgium international enjoyed a positive World Cup, helping his side to a third-placed finish in Russia, and now looks certain to stay in West London for another season.
After netting at least 12 league goals in the last four years, Sarri is confident that Hazard can now move on a par with Lionel Messi and Cristiano Ronaldo to become the world's best player.
"Hazard, technically, is really one of the best in Europe in this moment, I think," he told reporters. "He has to work from the physical point of view, of course.
"It depends on his position on the pitch. In the last five years, Cristiano has played like a striker. Messi like a striker, Eden sometimes like a winger. Eden can improve.
"We are talking about one of the most important players in Europe now but, in my opinion, he can improve more. He can be the first. It depends on him. The best for technical skill, the best for scoring, but I think it depends only on him. On his mind.
"Chelsea are one of the most important clubs in Europe. I think one of the most important clubs in Europe cannot sell an important player without the possibility of buying a player on the same level. The first time I have spoken to him, I was sure that he would stay. So I was concerned for 20 days, no more."
Hazard assisted Chelsea's third goal at Huddersfield Town last weekend after coming on as a substitute
