Hasenhuttl had been at the club for almost four years.
The Saints lost their sixth top-flight game in a row on Sunday, leaving them in the bottom half of the table. The assistant coach has left the club.
The Austrian took over at St Mary's in December of last year, making him the fourth longest serving manager in the league. He is the fifth top-flight boss to lose his job this year.
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"Hasenhuttl leaves having made a significant contribution to the club, overseeing some memorable results and also playing a key role in the development of our club infrastructure, identity and playing squad." We think it is time to make a change. Everyone involved with the club would like to express their thanks toRalph for all of his efforts as well as the dedication he has shown throughout his time as manager.
On an interim basis, Rubén Sellés will be the first-team lead coach. A permanent replacement will be announced in due course.
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In the span of 16 months, he was at the club, they lost toLeicester at home and then to Manchester United at home.
In his first season in charge, Hasenhuttl guided Saints to a 16th place finish, followed by an 11th place finish in the next season and a 15th place finish in the final campaign.
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When asked if this was his last game in charge, Hasenhuttl said he had made a lot of decisions. I don't have to do that.
We are not taking the reward for the effort on the pitch at the moment.
It's a reflection of what we've accomplished so far. It has not been up to par.
Sky sports' Dan Sansom.
You have to accept that we will lose a lot of games.
When I talked to Hasenhuttl at the training ground on Friday, he said those things.
He lost his job as manager of St Mary's after they were thrashed by the Jets.
After 14 games, the Saints are in the bottom half of the table. They have lost eight times in the first eight weeks of the season in the premier league.
He was used to pressure on the south coast. Two 9-0 defeats and several poor runs of form resulted in his position being questioned multiple times. The 55 year old was always bouncing back.
After spending £83m on new players this summer, the Saints have lost six of nine games in the premier league.
The team is fighting for survival. They're going down unless they improve on being more aggressive and willing to take one for the cause.
With Hasenhuttl still in charge, it wasn't worth taking that risk.