The deterioration could come from the fact that Kante is being played out of position - not in his favoured holding midfield role - and it apparently gives PSG hope that a deal could be done in the summer.
Hazard was deployed as a "false nine" in December when Chelsea beat City 2-0, ending a 21-game unbeaten league run for Pep Guardiola's side, but Higuain is likely to be the attacking focal point on Sunday.
And as Chelsea bid to hold off the challenge of Arsenal and Manchester United for Champions League qualification, Sarri feels Hazard and Higuain hold the key.
"Possession! Possession! The manager likes possession!" said Hazard, who spoke to The Times on a visit to a school for Chelsea Foundation talking about diversity and equality.
"I think they're so reliant on him that it might be they get that money then you can make a more rounded team rather than they just seem to be waiting on Hazard picking up the ball. I like this kind of football".
"In the moment he is really very determined", Sarri said of Higuain.
"We are still learning about his concept. It's a football feeling, I think". Though Chelsea succeeded before Hazard, and will go on to win plenty in the years post his departure, he's one of the top five players on the planet, and it's been a pleasure to see him in action in SW6 over the past six-and-a-half-years.
The Belgium global explained that all bosses want to see him on the score sheet. To that end, keeping the best goalkeeper in the world is essential.
"Managers like Mourinho, Conte, now with Sarri want me to score 40, 50 goals a season but can I do that?"
Hazard has contributed 12 goals and 10 assists in 24 Premier League appearances this season.
"No more, I think".