The 21-year-old has already played at international level for Republic of Ireland but finds first-team opportunities difficult to come by on Merseyside.
There were a host of clubs looking to take him on loan but Duffy believes he would learn more by staying at Everton and, with the injury to Phil Jagielka, he is hoping to get a chance soon.
Sylvan Distin and Jonny Heitinga were the two centre halves against Wigan in the FA Cup last week but Duffy is pushing for a start.
He said: "I'm just learning every day for when the manager needs me - this is why I'm playing in these Under-21s games. It's important to get some match action so that if he needs to throw me in then I'm alright.
"It's a good time to be around the team and we still have a lot to fight for in the league. It's good to be around such quality players and I would probably learn more here than if I went out on loan.
"I'm happy to wait for my chance at Everton and hopefully that will be soon."