In total, the 31-year-old found the back of the net 71 times in 94 appearances during his three year reign at the club after which he moved to the Allianz Stadium in a mega deal around £75m move to Juventus in 2016.
The Argentinean worldwide is now on loan at the San Siro from Juve but after starting life at Milan in superb form with 7 goals in his first 9 appearances, the striker is going through a dry spell having netted just once in his last 11 outings.
Higuain sent out on loan to AC Milan last August after the arrival of Cristiano Ronaldo and the Argentine has been unable to find his footing at the club.
Sarri has reportedly told the club that he wants Higuain, who is now on loan at AC Milan, having previously worked with the Argentine at Napoli.
"He had a tough moment, he has to put it behind him and get to work", said Leonardo.
Despite his recent struggles, Higuain's combined league record at Juve and Milan stands at 46 goals in 88 games - better than one in two.
"A goal can change things, but if he is to continue here, he needs to take on responsibility", Leonardo said, according to the Mirror.