I wouldn't think so. It used to be that, out of a group of 15 or 20 children starting kindergarten, five or six of them would cry all morning for several weeks when first enrolled. And that's one year older than your son. Now that most children have a lot of group experience prior to age 5, this doesn't occur so often. Even so, it is not a rarity.
The first thing I would do is make an appointment with the lead teacher in his group and get her suggestions. As the fall term is just beginning, she is probably not yet completely familiar with the strengths and weaknesses of all the children in her group, and she may not be aware of his difficulties in this area. Point out to her what you have noticed and tell her that he says he doesn't want to go to school. Your concerns will alert her, and she should then become more sensitive about helping him enter a group—which is a big challenge for a lot of 4-year-olds. She can put together small subgroups for a play session as a casual assignment and include him. Also, she can get into some of the activities herself and thereby make participation easier for him.
A second suggestion is to ask him which children in the group he likes the most. Then invite some of those children—no more than two at a time—over for play at your house, or take them together on an outing such as to the zoo. He may never be as out-going as some children, but these steps will help him get a start.
Our parenting advice is given as suggestions only. We recommend you also consult your healthcare provider, and urge you to contact them immediately if your question is urgent or about a medical condition.