Casey has returned from his loan spell at Swansea City in the Championship and joined Leyton Orient until the end of the 2025/26 season.
England U20 international Casey told Orient's website: “I’m really happy to be here. I grew up in Brentwood so Leyton Orient isn’t far from me and it is great to be joining somewhere with that local connection.
“My time at Swansea City was a great learning experience but I want to play regular football; I believe that Orient is the best place for me to get that whilst also helping the club to move forwards.
"I spoke to Lawrence Vigouroux and Ethan Galbraith, and they both only had good things to say about the set-up, the staff and the fans. That’s another reason I wanted to join and I can’t wait to get going.”