The Italy World Cup winner, who tore cruciate ligaments in his right knee in Sunday's 1-0 win over Catania, will have an operation on Dec. 19 and could miss the rest of the season.
"I will take it as a new challenge, a new battle to win. I have won many battles and I will also win this one," he told Italian television as he flew to Antwerp to meet top knee surgeon Marc Martens, who confirmed an operation was needed.
"I am really upset at what's happened but I think I will again be able to cut the recovery time. I always say that in life there are worse things, there is no need to despair."
Gattuso, 30, was tempted by a move to England in the close season but committed himself to Milan having helped the club win the 2004 scudetto and the Champions League in 2003 and 2007.
Milan, joint-second in Serie A this term, said before Gattuso's injury that on-loan Los Angeles Galaxy midfielder David Beckham would be the only new arrival in January.
Italy top World Cup qualifying Group Eight and look poised to be without Gattuso for at least March's visit to Montenegro.
