There is no such thing as an immortal man. That is a contradiction in terms. Humans, by nature, are quite mortal. The Bible frequently uses the expression “mortal man” – but never “immortal man.”
(This question may arise from a misunderstanding of what it means to be immortal. Humans may indeed live forever. However, merely having everlasting life is not what immortality is. After all, Adam and Eve were created with the potential to live forever. But they were quite mortal and died due to their disobedience. On the other hand, immortality means having life in oneself – possessing indestructibility and deathlessness.)
Since his resurrection Jesus is an immortal spirit. Paul stated that fact very plainly at 1 Corinthians 15:45, saying: “The first man Adam became a living soul. The last Adam became a life-giving spirit."
Jesus was the "last Adam" because he was the last perfect earthly son that God will ever produce. But since his resurrection from the dead Jesus is now a life-giving spirit.
The silliness of this sort of question is apparent when one considers the fact that those who believe that Jesus is still a flesh and blood man also believe him to be God Almighty. Yet, when Jesus was on earth he explained to a Samaritan woman that God is a spirit. What has happened so that God is now a man, according to the popular delusion anyway? People do not stop to consider the contradictions they embrace and espouse as the truth.
Paul, of all people, knew that Jesus was an immortal spirit. After all, when he was the Pharisee, Saul, he had a close encounter with the glorified Christ – an encounter that left him blind for three days.
So, then, why did Paul later say that God had appointed a man, Jesus Christ? Because, it was when Jesus was a man on earth that God anointed him to become the King, High priest and Judge. That appointment came about on the day Jesus was baptized and anointed.
Jehovah himself also describes himself in what is called anthropomorphic terms – in human terms, so that we may understand him better. He describes himself has having human features, like hands and fingers, eyes and ears, and feelings, etc. But God is not human. Never has been. Never will be. But Jesus has been. Although Jesus is no longer a man, he has had experience as a man and undoubtedly developed greater compassion for humanity having lived among us. And as stated, it was while he was upon earth as the Son of man that he gained the appointment to become King.
The absurdity of the notion that Jesus is still a man ought to be apparent to anyone willing to reason upon a few basic facts.
Consider, for example, that humans can only live in certain, very limited conditions. For instance, we have to breathe. Just a few minutes without oxygen and mortal man expires. Are we to assume that this immortal man in heaven has a steady supply of oxygen on hand? Also, we have to sleep regularly – typically eight hours per day. If deprived of sleep for just a few days people are prone to have a psychotic breakdown. And, of course, there is the matter of food and water and all the thousands of biological functions that go with that. Are we to suppose that the superman in heaven breathes and eats and drinks and sleeps and goes to the toilet and all the other things that go with being human? But if the believers in such nonsense suppose Jesus does not have any biologic needs or limitations, then in what way is he a man?