Having returned to pre-season training only 13 days ago, Hazard was on the bench for last weekend’s 3-0 win over Huddersfield, but came on and set up a goal for Pedro.
However, he is in line to start Saturday’s London derby against Arsenal, as Sarri seeks his first home win.
“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.
“Hazard, technically, is really one of the best in Europe at the moment. He has to work from the physical point of view, of course,” Sarri told reporters ahead of the game at Stamford Bridge.