The right-back had impressed throughout pre-season under both Eddie Howe and his successor Matthias Jaissle, filling in at right-back while Tino Livramento recovered from injury.
But with Livramento back in training and summer signing Amar Dedic making a strong start to life at the club following his move from Benfica, Newcastle used the extra time afforded by the Portuguese league's later transfer deadline to send the 19-year-old out for regular senior football instead.
Jaissle reportedly saw the move as too good an opportunity to turn down, with Arouca β who currently sit third in the Primeira Liga after a strong start to their campaign β offering Shahar the chance to test himself against the likes of Benfica, Porto and Sporting Lisbon over the course of the season. A Newcastle statement confirmed the switch: "Leo Shahar has completed a season-long loan switch to Portuguese top-flight side FC Arouca.
"Everybody at Newcastle United wishes Leo the very best of luck for the season ahead."
Born in Wolverhampton to an English-Israeli background, Shahar came through Wolves' academy before Newcastle signed him in 2023, and he was promoted into the senior squad last year after representing England at every youth level from Under-15 to Under-19.
He made his first-team debut as a substitute in February's Champions League play-off win over QarabaΔ, a moment Kieran Trippier was seen congratulating him for pitchside, and won an EFL Cup winner's medal with the club's development squad during the same period.
Reflecting last season on being initially held back from a loan move, Shahar had struck a patient tone about his path into the first team.
"I did not go out on loan in this window but I am happy now. I am in and around the first-team," he said.
"I got this opportunity to make my debut. I have to work hard whenever I play or train. If that's playing with the Under-21s I just have to keep working hard, and that is exactly the same if I get on for the first-team β I have to do the same."
That approach has now been rewarded with the kind of regular senior exposure a loan in Portugal is expected to provide.