The Croatia international, who joined the Portuguese outfit on a free transfer from Bayern Munich last summer, has only made 15 appearances in all competitions so far this season and has been linked with a move away from Lisbon for some time.The 31-year-old joins the Liga outfit on a temporary deal for six months, with Celta retaining the option to make the move permanent in the summer.
"When I got the offer from Celta, I didn't hesitate for a moment," Pranjic told a press conference on Tuesday.
"I believe I can bring a lot of experience to the team. Celta play very good football and I don't believe they should be so low down in the table."
The club's porting director, Miguel Torrecilla, added: "He's a purely offensive player. He can adapt to all kinds of midfield positions, be it on the wing, or in the centre next to a defensive pivot."