Belgium international Hazard starred for Chelsea last season, scoring 21 goals and providing 17 assists across all competitions.
His form earned him a move to Real Madrid, while Sarri, who won the UEFA Europa League and led Chelsea to a third-place finish in the Premier League, left for Juventus.
Sarri's first and only season at Stamford Bridge looked to have been a success, but issues over his playing style proved a sticking point throughout his tenure.
The Italian believes that having to find a way to play Hazard in his preferred role meant he could not deploy the free-flowing, 4-3-3 system that had drawn plaudits during his time at Napoli, and also caused problems in defence.
"In recent years, I've had 4-3-3, but the 4-3-3 at Chelsea was very different to the one at Napoli," Sarri said.
"We had to accommodate Hazard's characteristics, as he could change the game, but also his presence caused issues in defending that we had to work on."
One player that Sarri brought to Chelsea last season was Gonzalo Higuain, who joined on loan from Juve in January.
Higuain was a crucial player in Sarri's Napoli side before he left for Juve in 2016, and Sarri is looking forward to another reunion with the 31-year-old, should the Argentinean wish to remain in Turin.
"You know I love [Higuain] a lot. I have always been very supportive. It depends on him," Sarri said.
"In terms of the other players at Juventus, I have to be very modest because here there are staff who have been dealing with them for many different years.
"I think it's absolutely fair that I listen to them, then we'll make a decision together. The staff know the players better than me - maybe Higuain is the only one I know slightly better - so it will be up to me to listen to them and adapt."