The 33-year-old midfielder has been training with the relegation strugglers for the last two weeks and has now signed a short term four month deal, which could be extended later this summer should the club remain in Spain's top flight.
The report confirms Ghanasoccernet.com's exclusive report last week that the enforcer had been offered a contract after impressing while on trial with the club.
The former Ghana worldwide found himself without a club, having left Pescara last summer, where he made just nine appearances in a largely disappointing spell with the lowly Italian club.
The Ghana star is a free agent and can therefore be signed immediately, despite the transfer window being closed.
Starting out with Liberty Professionals in his native Ghana, Muntari landed in Europe after that U-20 World Cup with Italian club Udinese.
He won the Champions League at Inter Milan with two league titles under his belt after playing for English sides Portsmouth and Sunderland.
Branquiazuis are now in 19th place, three points adrift of safety, with 14 league games remaining in the 2017/18 campaign.