Durham coach Geoff Cook is in a "critical but stable" condition after suffering a heart attack on Thursday.
The 61-year-old remains in hospital undergoing treatment.
A brief statement from the county on Friday read: "Durham Head Coach Geoff Cook suffered a heart attack yesterday. Geoff remains in hospital and his condition is critical but stable.
"The club has been inundated with well wishes for Geoff through social media and our thoughts continue to be with Geoff, Judith and his family."
Durham skipper Paul Collingwood and former England captain Michael Vaughan among those offering support on Twitter.
Collingwood posted: "All our thoughts with Geoff Cook and his family. Sad sad day."
Vaughan added: "Thoughts and prayers are with Geoff Cook and his family...A great man.. Get well soon Geoff..."
England spinner Graeme Swann wrote: "Just heard the news about Geoff Cook. Fingers crossed for a speedy recovery for him."
England wicketkeeper Matt Prior added: "Thoughts are with Geoff Cook and his family at this time. Fingers crossed for a full and speedy recovery."
Cook played in seven Tests and six one-day internationals for England in 1982 and 1983 and became director of cricket at Durham when they became a first-class county in 1991.
He was named as head coach in 2007, and has guided them to the Friends Provident Trophy, before they won back-to-back county championship titles in 2007 and 2008.