Real Madrid were keen to sign Hazard in the summer transfer window, but Chelsea refused to play ball and the Belgian, unlike countryman Thibaut Courtois, did not push to leave.
The 27-year-forward who has been at Chelsea since 2012 has made a huge impact at Stamford Bridge, helping the club to several trophies, including a pair of Premier League titles.
Coach Sarri will likely start his first-team players with Kepa at the goal post, Azplicueta, Rudiger, Luiz, Alonso at the defense, Barkey, Jorginho and Kante at the midfield, Hazard, Pedro and Giroud at the front.
Mourinho has tasked Ander Herrera and Scott McTominay with the responsibility of man-marking Hazard in recent times but insists that Maurizio Sarri has many other unsafe players at his disposal.
"For me, those games are the best games to play", he added.
"The game is going to be very hard, we're playing away".
"And we want him to stay and we'll do what we have to do to entice him to stay". But I don't know if they're capable of that at the moment.
'Yeah, I think so because the last three years it has been like this, ' the Belgian said.
"There was that penalty and then a fine David De Gea save, so United really could have been 4-0 down at half-time. In the last three days I have seen him very well in training, very very well". "So I think for his father, probably the Europa League is not important, but for us it is important". "I am completely focused on improving my team and my players".