"Deciding to leave Milan's bench is not easy. But it's a decision I had to make.
"There was not a precise moment in which I made it, it was the sum of these 18 months as coach of a team that for me will never be like the others. Months that I lived with great passion, unforgettable months.
"Mine is a painful but thoughtful choice.
"Am I giving up a two-year contract? Yes, because my story with Milan can never be a question of money."
Gattuso had recently told DAZN (h/t Burton) the pressure was getting to him: "I've barely slept in the past 18 months, mentally I'm in pieces."
He makes way after the Rossoneri missed out on UEFA Champions League football.
The Italian side also exited the UEFA Europa League in the group stage on goal difference, having taken 10 points from their six matches.
Gattuso took the Milan position midway through the 2017-18 campaign following a tough start to the season for the Rossoneri. Despite his limited managerial experience, he was able to get more from the players than predecessor Vincenzo Montella and steered Milan to sixth spot, as well as the Coppa Italia final.
As a result of his fine work, the Italian was handed the job permanently at Milan and signed a contract until 2021.
Despite bringing in the likes of Gonzalo Higuain—who left in January and was replaced by Krzysztof Piatek—Pepe Reina, Mattia Caldara and Samu Castillejo in high-profile summer transfers, the team struggled to find consistency and were held to 11 draws.
Here's a look at his overall record:
While the Milan fans will be hopeful a new manager brings in some fresh impetus, the club still have a long way to go before they can be considered one of the major forces in European football again.
For so long, the San Siro outfit have been without direction. On the pitch, they have made numerous costly acquisitions seemingly without a plan of how to get the best out of the new players. In terms of managers, no one has been in place long enough to get a blueprint instilled to aid the team's progression.
Gattuso lit a fire under Milan when he first arrived, although he seemingly lacked the tactical acumen and man-management skills needed to succeed when those flames ceded. Still, whoever replaces the 41-year-old has a massive task on their hands to get the Rossoneri challenging for prizes again.