His post has since attracted more than 3,000 reactions and hundreds of comments slamming McDonald's.
"Omg I'd be throwing it back at them. That is shocking. And make a call to the health department too," one person wrote.
McDonald's has since responded to the man's complaint, telling the Herald staff swiftly apologised and dealt with the complaint immediately.
"Incidents like this are extremely rare and we treat them very seriously," they said.
"When the customer returned the product restaurant staff apologised immediately, and followed investigation processes, including checking daily food safety reports and reviewing CCTV.
"At this stage it appears the cause was human error.
"In the 30 million plus orders we've handled this year, we've had fewer than 20 complaints relating to undercooked food. Regardless, we constantly look at ways to reduce of incidents like this occurring."
It appears the post has since been removed from McDonald's Facebook page.