The 19-year-old will spend the remainder of the 22/23 campaign at Priory Lane, helping The Sports in their challenge for the promotion play-off places in the National League South.
Bartley is a powerful centre-back who is also capable of filling in at right-back if needed. He notched eight appearances and kept three clean sheets for the Under-18s side during the 2020/21 title charge.
He went on to make a further eight appearances for Rob Quinn’s Under-18s in 2021/22, along with captaining the side during the Premier League Next Generation Cup in pre-season of 2022/23.
The defender signed his professional contract with the club in July 2022 and has featured twice for the Under-21s this season against Hertha Berlin and Sheffield United.
Commenting on the loan move, Academy Director Gary Issott said: “We wish Ryan the best of luck with his loan move to Eastbourne Borough. We hope Ryan can establish himself at Eastbourne and get some much needed game time."