Martinez paid for a 4-1 drubbing at home to Levante with his job on Sunday, and less than 24 hours later, Sergi has been installed as the man to turn around their season.
The Andalusian club sit 18th in La Liga, without a win in seven league games.
Sergi, winner of three league titles and two Copa de Rey crowns in his playing days at Camp Nou, has previous coaching experience with Barca's youth teams and Recreativo Huelva, where he spent two years before resigning in May last year.
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