He has some money but if he buys a car with it he will not be able to do Hajj

Praise be to Allah.

If you need the car, there is nothing wrong with buying it even if that causes you to delay doing Hajj, because one of the conditions of Hajj being obligatory is that one can afford it, which refers to having wealth surplus to ones basic needs. One of these needs is a car to travel in, the price of which is within his means, without going to extremes and buying something extravagant in imitation of others or to show off. For the conditions of Hajj being obligatory, please see the answer to question no 41957. 

But if you do not need the car, then you should give Hajj precedence over buying a car. 

We ask Allaah to bless you abundantly and grant you a good and blessed provision.  

And Allaah knows best.