The 34-year-old has not played since being substituted during his side's Serie A opener against Lazio on 9 September.
Gattuso collided with team-mate Alessandro Nesta and was later diagnosed with sixth nerve palsy, a disorder associated with the dysfunction of the cranial nerve that controls eye movement.
A Milan statement read: "After two days off the Milan players were back in training today at Milanello at 3pm. With 13 players missing it wasn't the usual training session, although there was one piece of good news.
"Rino Gattuso, whose health has been steadily improving, joined the rest of his team-mates for the session."
Fellow midfielder Mathieu Flamini, who has not played since suffering knee ligament damage in pre-season, also trained with the group again and could be in contention for this weekend's game at Palermo.