Rob Halhead had already eaten some of the Dolmio Stir-Fry Pasta Sauce in Sundried Tomato Flavour when he found what he describes as the unidentified 'fibrous' chunk.
The chunk has not been tested yet, and so has not been identified.
"The sauce is marked as suitable for vegetarians," Halhead told Plant Based News, "but all the ingredients are vegan.
"I was eating the sauce with pasta when I found the chunk, which has a swirly fibrous look to it, like tuna. I felt pretty disgusted really, and confused."
Halhead contacted Mars (which owns Dolmio) and was asked to send the chunk in for testing.
'We cannot speculate'
"We take all complaints seriously and have requested the return of this product so we can conduct an investigation and identify the object in question," A Mars spokesperson told Plant Based News.
"We have not yet received this from Mr Halhead so cannot speculate at this time as to what it might be."