Duffy initially joined the Glovers in late September but his spell in Somerset has now been extended until the end of November.
The 21-year-old has made five starts at the heart of Yeovil's defence and has impressed manager Gary Johnson.
"He is a good player and he needed the games," Johnson said. "He doesn't mind competing and he has a little snarl when he needs it which is good.
"I'm looking forward to him putting a header in the back of the net soon, he deserves a goal and hopefully he will get it on Saturday."
- Sports & Recreation