What are the chances of getting pregnant from withdrawal method 4 days before ovulation?

Less likely : You are cutting it close but less likely than if he had ejacualted.

Possible: In general sperm are still around 2-3 days after intercourse and with withdrawal at least a few drop of pre-cum end up in the vagina. Each drop has about 20 million sperm. Day four there could still be a few available for fertilization. Withdrawal is not a good way to prevent pregnancy. Think about a condom or at least a spermicide like vcf.

Too high: The withdrawal method is not a method. It is an excuse for not planning. Sperm can remain viable for long enough to occasionally penetrate the ovum causing pregnancy. There are better ways to prevent conception and avoid the worry and ultimately the responsibility of dealing with the aftermath of an unplanned pregnancy.