He will need supplemental heat, so you can set him up a hospital area with a brooder. Cleanse the wound with soap and water, and a dab of hydrogen peroxide. Then apply a VERY thin layer of Neosporin...with NO lidocaine or benzocaine. Keep him separate from the others until he is larger and the wound is healed. That is really young and small for a Silkie to be introduced to adults, in my own opinion...I don't introduce until they are several months old myself! I turn out all of the chickens, and then release the newbies, so they all forage together. That way they meet on neutral territory.
Keep him warm (think about 80 degrees or so), and be sure he can get away from the heat, too. Just like a brooder! Let him rest and don't force him to do anything yet, you'll just stress him out. Give him food and water and once he gets nice and toasty and overcomes the stress of being attacked, I bet he'll be eating/drinking by this evening. Apply the Neosporin 1-2 times a day on the wound in a very thin layer. :0)
Good luck!