The club are providing support to the family of the 68-year-old, who retired in 1991 to start a successful career as a television pundit with the BBC.
"The thoughts and support of everyone at Liverpool FC are with our legendary former captain Alan Hansen, who is currently seriously ill in hospital," a Liverpool statement read.
"The club is currently in contact with Alan's family to provide our support at this difficult time, and our thoughts, wishes and hopes are with Alan and all of the Hansen family.
The thoughts and support of everyone at Liverpool FC are with our legendary former captain Alan Hansen, who is currently seriously ill in hospital.— Liverpool FC (@LFC) June 9, 2024
"We will provide any further updates as we receive them in due course, and we request that the Hansen family's privacy is respected at this time."
Hansen joined Liverpool from Partick Thistle in 1977 and won three European Cups, eight league titles, two FA Cups and three League Cups in 620 appearances for the Anfield side.
Hansen's former Match of the Day colleague Gary Lineker wrote on X: "Horrendous news. Thoughts are with Alan, Janet and all the family."
The BBC's Match of the Day account said: "The thoughts and prayers of everyone at Match of the Day are with Alan and his family at this difficult time."
Ex-teammate John Aldridge, chairman of the former players' association Forever Reds, also sent a message of support.
"All our thoughts as ex-LFC players are with Alan (Jocky) Hansen and his family. Let's hope he can pull through his illness. ynwa," he wrote on X.
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