Celtic boss Neil Lennon is "hoping and praying" for the recovery of former Hoops team-mate Jackie McNamara.
The 46-year-old was taken to Hull Royal Infirmary on Sunday night after collapsing outside his home in York and is said to be in a critical but stable condition.
Lennon, who played alongside McNamara during the early 2000s, said: "I am lost for words, I don't know what to say. I spoke to him on Tuesday so I am devastated by the news and hoping he pulls through.
"People have been keeping me abreast of things. He is a strong guy, a great guy and a fit boy for someone of his age.
"He has been fit all his life so I am hoping and praying he comes through OK."
A spokeswoman for Hull University Teaching Hospitals NHS Trust said: "We can confirm Jackie McNamara was admitted to Hull Royal Infirmary on Sunday night and is currently being cared for in our Intensive Care Unit. He remains in a critical but stable condition.
"We are supporting both Jackie and his family, who request their privacy to be respected at this time."
Lennon is just one of several former team-mates of McNamara who have been sending sent their best wishes since news of the former defender's serious illness emerged.
Simon Donnelly, McNamara's former Celtic team-mate, managerial assistant and co-owner of a pub in Spain, simply posted images of praying hands, hearts and a strong arm to show his thoughts.
Parkhead hero Henrik Larsson, who played alongside McNamara at Parkhead for seven years, posted a picture of McNamara on Instagram with the message: "He needs all the love we can give him. @jackiemac4 keep on fighting."
Ex-Rangers manager and striker Ally McCoist, a former Scotland team-mate, posted on his Instagram account: "Rooting for you @jackiemac4, always a battler. With you and your family all the way."