The Argentine has been missing since October with a calf injury, but was back for the win over Cagliari.
"I'm very happy to be back and to be with the boys," he told Milan TV.
“I was happy to return to the squad after such a long time. It's important to come back, and what matters is that the team is healthy.
“My contribution depends on the Coach. We must give 100 percent, both those who play and those who don't, for the good of the team."