Theodore knew that Zach had come in with him, but he had completely forgotten about him now. His focus was entirely on Neville, on performing a series of diagnostic spells that (ironically) Rosier had taught him.
He didn't think he had enough time to heal everything. He certainly couldn't do much of anything about the visible wounds since he hadn't come with a plan to spring Neville from imprisonment, and there was nothing particularly clever he could come up with on the spot. But he could do something for the injuries that were less visible, to make Neville a bit more comfortable, help him hold out just a little bit longer.
"Drink this first," he said, reaching into his bag for a potion to relieve the pain, and lifting it to the bound servant's lips. "It'll take some of the pain away."