Gattuso: Higuain has not asked to leave
Higuain joined Milan on loan from Juventus in August for a fee of €18million with an option to buy him outright at the end of the season.
However, the move has not panned out as expected, with Higuain scoring only six times in 15 Serie A appearances for Gattuso's men.
He ended a run of nine games without a goal, which featured a missed penalty and a red card against Juve in November, last month but has been heavily linked with a reunion with Maurizio Sarri at Chelsea.
There have been reports Higuain could be dropped for Wednesday's Supercoppa Italiana clash with Juve ahead of a move to Stamford Bridge.
But Gattuso told a media conference: "I base my decisions on how players train during the week and how they work with the staff and their team-mates.
"At this moment, I have to repeat the same words: there are many rumours, but Higuain is training well, working with everyone just fine and is at our disposal.
"We'll see tomorrow whether he plays or not. He has to decide what to do, how to resolve this issue, but right now he is training with great professionalism. We'll see.
Final training session for the Rossoneri as the showdown draws nearer
La rifinitura dei rossoneri a Gedda: -24h a #JuveMilan! #Supercoppa pic.twitter.com/6bfWnTsb5H
— AC Milan (@acmilan) January 15, 2019
"If he plays, it's because I see him in good shape and relaxed. Either he's a great actor or he's really within the team, is always chatting and kidding with his team-mates.
"I agree that after the missed penalty and red card against Juventus, something happened in his head. We'll see tomorrow. As I said, it's not easy for a coach to change the idea of a player, so I have to concentrate on putting out the best line-up for the situation and getting the best out of every player.
"I want to reiterate that Higuain has never told me he wants to leave. I am waiting for that.
"I want to be honest, I didn't even want to talk about Higuain, as we're here for the Supercoppa. That seemed the fair thing to do for a team.
"I am not upset. I too was a player for many years, I realise there are moments when we all see things differently and cannot judge how someone else thinks.
"If the glass is half-full or half-empty, it remains the same glass. We'll see what happens. I want to see this Supercoppa, I hope it is a great game for us, but I won't be upset or let down if he goes."