The Belgium international, who returned late to Stamford Bridge following his nation's third-place finish at the World Cup, has been heavily linked with a move to Real Madrid.
Sarri has opted to bring Hazard on from the bench in both of their Premier League games so far, and the attacker played a key part in securing wins against Huddersfield Town and Arsenal.
"It's clear," the Italian told Sky Sports News. "He is a great player, but I think that in this moment he is not able to play for 90 minutes.
"So I think that it was better for 25, 30 minutes when the intensity of the match is going down. But I hope, one more week, maximum two weeks, he will be able to play for 90 minutes."