The Saints have taken the 21-year-old shot-stopper on a short-term agreement through to the end of the 2016-17 Premier League campaign
Southampton have completed the signing of Mouez Hassen on a five-month loan deal from Nice.
The 21-year-old has previously worked with Saints boss Claude Puel in France and will provide added competition between the sticks.
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Hassen arrives at St Mary’s having made 50 senior appearances for Nice and boasts France international experience at every youth level from U16s up to the U21 set-up.
He is looking forward to taking on a new challenge in England and settling into new surroundings.
Hassen told the club’s official website: “I am really happy. It’s a pleasure for me to come to England for the first time and I am really happy to get to know the Premier League.
“I am really looking forward to joining the team.”
Executive Director of Football Les Reed added: “Mouez is a promising young goalkeeper, and we are very pleased to have been able to bring him to Southampton.
“He has built an excellent reputation during his time with Nice and also in his country’s youth teams, and will provide us with further depth in the months ahead.
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“As well as adding to our squad, we believe Mouez can continue his development in his time at Southampton and make strides in his own game under the expert guidance of our Head of Goalkeeping, Dave Watson, as well as working alongside Fraser Forster.
“Harry Lewis has had opportunities and gained great experience while Alex McCarthy has been injured, and Stuart Taylor has brought excellent experience to the group, and now Mouez will add to our strength in depth.”