He said he was going to shrug it off and continue eating the bread, but decided to break apart the slice just in case.
It was then he found three more shards of glass, he said.
"They were very small, but they were enough that you knew exactly what they were," he said.
Timu contacted Foodstuffs and Flaxmere New World's owners had apologised to him, he said.
Foodstuffs spokeswoman Antoinette Laird said the bread would be sent to an independent lab for testing.
"Once this process has happened we will be in a position to confirm if the offending particles are in fact glass, and if so what type of glass.
"Fortunately, we have had no other reports of issues from customers so this appears to be an isolated incident – but we would encourage any customer who has a concern to reach out to our customer services team on 0800 245 114, who are more than happy to assist."
A second complaint from the same batch would trigger a product recall, the spokeswoman said.