Preliminary lab test results have indicated that a McDonald's Sausage McMuffin burger which allegedly contained a lizard is "100 percent chicken".

A photo of the burger with the lizard-like tail sticking out of it went viral on the Internet this week, but the fast food chain said on Friday that it was actually a chicken blood vein.

Said McDonald's senior communications manager Kevin Lim: "The vein is white in colour because of the Halal slaughtering process where blood had to be drained."

He added that the lab report has been shared with the relevant authorities. The restaurant's chicken sausage patties are made from minced dark and white chicken meat and are imported from Malaysia. "We have also traced back the product's production process and no product from the same batch had any quality issues reported," he said.

The Straits Times reported on Friday that McDonald's had collected the half-eaten burger from the customer who posted the photo on Facebook.

The customer, known only as Sandy Sand on her Facebook page, had said the burger was bought from the Ang Mo Kio drive-through branch. McDonald's later issued an apology for her experience.