'Would you like slugs with that?'

Eric Lin was less than impressed by the contents of his McDonald's salad - even less so when when he was given expired Big Mac vouchers as compensation. Photo / supplied

A North Shore man has been given expired Big Mac vouchers as part of his compensation after finding a slug "the size of a human fingernail" in his McDonald's salad.

Lintek worker Eric Lin bought the garden salad from the fast food giant's Constellation Drive restaurant at lunchtime on Tuesday.

The 29-year-old McDonald's regular had eaten through about half the meal when a squirming mass caught his eye.

He looked down and saw a large black slug burrowing its way through the lettuce on his fork.

"I just felt like puking - but I couldn't puke. It certainly stopped my appetite for the rest of the day.

"It's about the size of a human fingernail so it's probably been in there some time."

Mr Lin said he made a complaint to McDonald's head office soon after he found the slug.

The company got in touch with him to apologise yesterday.

It sent a worker to collect the salad box - with the slug still inside - and left him with $30 in meal vouchers and two expired Big Mac vouchers.

McDonald's spokeswoman Kelly Armitage said the company was taking the incident "extremely seriously".

"Our customer services team has contacted Mr Lin, apologising for his experience at our Constellation Drive restaurant."

Ms Armitage said she could not speculate as to how the "foreign object" had made its way into Mr Lin's salad.

The company would be talking to its suppliers as part of a thorough investigation into the incident, she said.

"Incidents such as this are extremely rare and we will be communicating with Mr Lin throughout our investigation."