The 43-year-old replaces Juan Ignacio Martinez who was sacked after just four months in charge following Almeria’s 4-1 drubbing by relegation rivals Levante on Sunday.
The Rojiblancos are now without a win in seven games stretching back to early February.
With nine games to go, Almeria, sitting on 18th and one point adrift of safety, have turned to the former Spain left-back to help rescue their flagging season.
Sergi is Almeria’s fourth coach of the season and his first game in charge will be on Wednesday when he takes his new side to the Nou Camp to face league leaders Barcelona.
The 43-year-old made his name as a player (1992-2002) and started his coaching career as a youth coach (2009-2011) at Barca before taking a role at Segunda Division side Recreativo Huelva.
On top of their league woes, Almeria also face being hit with the deduction of three points by FIFA for failing to pay transfer fees owed to foreign clubs, although the Andulacian club are appealing that decision to the Court of Arbitration for Sport.