Retail giant Wal-Mart has launched an investigation after a 5-year-old boy said he was pricked by a 3-inch hypodermic needle left inside a shoe.

Instead of telling his mother about the needle right away, Nathan Pidcock put it in his pocket and showed it to her the next morning. As a precautionary measure he has had to undergo HIV and hepatitis tests.

The world's largest discount retailer has so far refused to comment on the incident.

But the boy's mother Rebecca Pidcock says the Wal-Mart has told her it cannot be held liable because it did not happen inside the store.