The Norway international will make his return to Spain with the Galician club, just five months after leaving Real Sociedad for the Bundesliga.
And Demidov already intends on staying long enough to make a good impression.
“Hopefully I can stay beyond June 30 and do everything I can to help the team. At a good club like this, players need competition. If there wasn’t any, this would not be a great club,” he told the club's official website.
The 26-year-old made the switch to German side Frankfurt in 2012, however, he failed to make much of an impact on the first team, making just five appearances for the club.
The centre-back will be hoping for a change in fortune whilst on loan to help his new side climb up the Liga standings.
He added: “I’m very happy because I’ve come to an historic club."
Celta currently sit just above the relegation zone in 17th place and face Valladolid on January 6.