The left-back agreed fresh terms with the Reds before returning to the Welsh capital for another temporary spell.
The 21-year-old appeared eight times for the Bluebirds during the second half of last season, helping them earn promotion to the Championship.
Brian Barry-Murphy's side host Wrexham in their league opener on Monday night.
Scanlon has played two competitive matches for Liverpool's senior team to date, having arrived at the Academy set-up from Birmingham City in 2021.
