Per The Independent's Luke Brown, Gattuso went to bring on Bakayoko in the first half following an injury to Lucas Biglia, but the Italian said that after "seven or eight minutes, he still had not put on his shin pads," so he opted to use Jose Mauri instead.
Bakayoko gave his account of the events on Instagram (h/t Brown):
"Despite starting on the bench I was ready to give 200 per cent even if I only played five minutes tonight.
"When Lucas [Biglia] began to suffer on the ground, I was asked to prepare for the change. So I prepared myself immediately and went to warm up for a maximum of two to three minutes.
"Then I was asked to return to the bench. everything passes I think between 23 and 26 minutes.
"It was when I sat on the bench that the coach spoke to me in unexpected terms and I only repeated his words. Nothing more."
Reports quickly followed a heated confrontation between coach and player on the bench, in which Bakayoko appeared to tell Gattuso to "f--k off:"
In his Instagram statement, Bakayoko added:
"Let me be clear: I have never refused to come into play and I do not have to drag myself to warm up. It seems to me that the images speak for themselves.
"I had only one desire which was to enter the field and help my team-mates as I have always done and as I will do until the end of the season. Forza Milan."
Bakayoko has been on loan with Milan from Chelsea this season after a disappointing debut campaign with the Blues.
After a somewhat rocky start at the San Siro, the 24-year-old had settled into some strong form in recent months.
Premier Sports shared one of the highlights of a fine performance he put in during Milan's 1-0 win over Lazio in April:
However, Monday's incident capped what had already been a week to forget for the Frenchman, per Mediaset (h/t Bleacher Report's Alex McGovern):
Picking up maximum points will be vital if they are to secure UEFA Champions League football for next season.
Whether Bakayoko features for the Rossoneri again in this campaign could offer an indication as to whether he might remain at the club this summer.