I don't see any chance to improve the situation

unless he has solid proof of his consistent good performance before or other managers he worked with support him. Another chance is to internally transfer to other departments before things go ugly -- this is not easy when the current manager is on odd with him. I would suggest quit and look for new job if his has no problem with visa or greencard etc. Otherwise it'll soon be he gets fired for sure no matter how hard he tries. He probably will get a package(not big one) but the drawback is that there will be some shadow on him in the HR system. For the exit solution, there is some chance to negotiate with the current manager for a good reference and get an employment letter for EI purpose even it's he quit. It has not much to do with the friend's real performance. It's just the new manager does not like him.