The 34-year-old had not featured for the Rossoneri since the opening Serie A match against Lazio after being diagnosed with an eye problem following a collision with team-mate Alessandro Nesta.
He came on in injury-time in Milan's 2-0 victory against Parma on Saturday, and he admitted after the game that he is eager to return to work after more than six months on the sidelines.
"An ordeal is over," Gattuso told Radio DeeJay.
"With all the cortisone shots I got I look like a boxer, but I am so eager to train."
Milan remain four points clear at the top of the Serie A standings, with Juventus coming in second after their 5-0 demolition job of Fiorentina on Saturday.