The young centre-half will link up with the English League Two side for the remainder of the 2023/24 campaign.
After making the switch to Hibs in the summer, Riley has gone on to make two appearances with his league debut coming against Livingston back in August.
He will now link up with Danny Cowley’s U’s who sit 22nd in the fourth tier of English football.
On the loan move, Hibernian FC Head Coach Nick Montgomery commented: “At this stage of Riley’s career it’s imperative that he goes out and gains regular football.
“Gametime has been limited for him this season and he needs to continue developing. We hope he embraces this challenge and it’s a successful loan spell where he plays week in, week out.”
