That leaves Saints looking for the 10th new manager in just eight years, after the Dutchman cut his contract three years short.
Southampton, who had their highest Premier League finish ever under Koeman last season, have qualified for the Europa League group stages this season, but will entice a few big names?
So who is in the frame to be sat in the manager’s seat when Watford come to St Mary’s on opening day?
Frank De Boer
After leaving Ajax after missing out on his fifth Eredivisie title, he was heavily linked with a move to England for the vacant Everton job, but now Koeman has moved to Merseyside and he is favourite to be in the dugout next season.
Frank De Boer was also assistant manager for Holland during the runners-up place at the 2010 World Cup in South Africa, which gives him invaluable experience.
The 46-year-old loves to play a possession game and is very tactical due to his playing career with spells at FC Barcelona and Ajax.
Trophies won as a manager: Eredivisie x 4, Johan Cruijff Shield
The youngest manager in the Premier League ever has cemented has name into football with an outstanding season and defying all the odds and keeping Bournemouth up in their and his debut season.
He established a fantastic team effort after winning the Championship, and picking up some serous injuries to key players he was able to work some magic and produce some great football and see the Cherries through to their second season in the big time.
The 38-year-old wouldn’t have to move far just being down the road from Southampton, but his style of play would fit perfect for this club, which could result in a successful era on the South Coast.
Trophies won as a manager: Football League Championship
Moyes has been unemployed since leaving La Liga side Real Sociedad and surely must be searching for a return to England.
His time at Manchester United wasn’t lived up as much as it was hyped but his time with Everton was great, he turned them from a sinking ship to a sustained sailing one, but is Moyes what we need?
Trophies won as a manager: Football League Second Division, Community Shield
Emery has just vacated is post at Europa League Champions Sevilla and was strongly also linked with the Everton job also. He led Sevilla to three consecutive European titles.
The 44-year-old has had successful stints with Valencia and Spartak Moscow, and not just at his time at Sevilla and his arrival at Saints would be an idea one. I think he’s the man for the job but if he has left his beloved Sevilla, is there a job already lined up for him?
He plays entertaining attacking football but also loves to play a solid 10-men behind the ball defensive game, but he honestly could return Saints into the title challenging side of the 80’s.
Trophies won as a manager: Europa League x 3
Vitor Pereira is currently Fenerbache coach and has been linked heavily over the last couple of days to the vacant Saints job.
He has enjoyed spells at three of Europe’s biggest clubs with a huge demand by the fans. Coaching Porto, Olympiakos and now Fenerbache.
He is a very passionate individual on the side-lines, something that the English game and lacks and would offer something different to the club with his arrival.
Trophies won as manager: Primeira Liga x 2, Supertaça Cândido de Oliveira x 2, Superleague Greece and Greek Football Cup.