i would take some of the water from the main tank he is in right now and fill the other tank with it depending on the size of the two tanks. melafix would be a good med to use on his injury. do water changes of about 10% once a day, then add the meds. if you are using a filter, do not add carbon to the filter. once he is looking like he is healing you could add him back to the main tank. about 2-3 weeks. you could also add some salt to the water also. one round tablespoon for every five gallons of water. would move him though. the other fish do not need to be medicated and the plec will not be able to tolerate the salt if you decide to use.
also use aquarium salt as table salt has iodine in it. fish are intolerable of iodine.