Southampton midfielder Oriol Romeu will undergo ankle surgery that will keep him out until the end of the season.
Romeu, who has impressed with his ability to break up play and recycle possession in the Southampton engine room since his arrival from Chelsea in 2015, has made 20 Premier League starts for Hasenhuettl's side this season.
The 29-year-old Spaniard was forced off in the 70th minute of Tuesday night's 3-0 defeat by Leeds United.
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"Oriol Romeu's season is over. Surgery on Monday means three months out," Hasenhuettl told a news conference.
"He has a fracture on his ankle and definitely this season is over for him. It will take a minimum of three months until he is back."
Hasenhuettl feels the injury crisis at the club is a "never-ending story", with on-loan Liverpool forward Takumi Minamino also ruled out of Monday's trip to Everton because of a hamstring problem.
Kyle Walker-Peters, Theo Walcott and Ibrahima Diallo have suffered injury setbacks in recent weeks, while youngsters Michael Obafemi and William Smallbone are long-term absentees.
"We are not the only team which struggled with injuries, but for us it has hurt us very much this season, yes," Hasenhuettl said.
After climbing to the top of the league table in November, Southampton have dropped down to 14th and are without a win in their last seven games in the competition.
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