The highly-rated 19-year-old, who has won seven caps for Croatia and become his country's youngest-ever player when he made his debut at the age of 16, joined Barca from Dinamo Zagreb last year.
The attacking midfielder spent most of his first season playing for Barca B but made his first-team bow against Elche in the Copa del Rey in January and was included in the senior squad for the pre-season tour to America, where he featured in all three matches.
Gijon announced the move in a statement: "Sporting have secured the services of the Croatia attacker Halilovic from Barcelona on loan for the rest of the season.
"He is set to take part in training alongside his new team-mates on Saturday morning. His official presentation is set to be at the end of the session."
Gijon, back in the top flight after an absence of three years, hosts Real Madrid in its Primera Division opener on Monday morning (AEST).
