Relegation-threatened Livorno have sacked Domenico Di Carlo after just 88 days in charge and re-appointed Davide Nicola.
Virgil van Dijk claims he knows nothing of interest from English clubs and is keen to prove himself in the Champions League with Celtic.
The 23-year-old centre-back will hope to play regular football after signing a three-year deal with the Galician club on Thursday, with Barcelona reserving a buy-back option as well as rights on any future transfer.
Fontas was promoted from the Catalan club's B team in 2011, but a serious knee injury the following year hampered his chances of breaking into the first team and last season he was loaned out to Real Mallorca, with whom he made nine appearances.
"Celta have chosen me and that made me decide to come and sign a three-year contract," he said on Celta's official website.
Celta Vigo managed to avoid relegation from La Liga on the final day of last season and have turned to former Barca midfielder Luis Enrique as their coach for the next campaign.