The Saints currently sit 18th in the top-flight table after 14 games and have won just three matches so far in 2022/23.
Southampton have been mulling over a managerial change for a few weeks, but it was thought they could wait until the World Cup break - which starts next week.
However, the club have instead acted swiftly in the wake of Sunday’s 4-1 defeat at home to Newcastle and Hasenhuttl, who has been in charge since December 2018, was sacked on Monday morning.
“Southampton Football Club can confirm it has parted company with Men’s First Team Manager Ralph Hasenhuttl,” read a Southampton statement.
“First Team Assistant Coach Richard Kitzbichler has also today left the club. Hasenhuttl, who was appointed in December 2018, departs 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.
“However, we now believe it is an appropriate time to make a change. Everyone involved with the club would like to express their sincere thanks to Ralph for all of his efforts, as well as the unwavering commitment he has shown throughout his time as manager.
“First Team Lead Coach Ruben Selles will take charge of the side on an interim basis for our game on Wednesday night. The club will be announcing a permanent replacement in due course.”