Birmingham City boss Karren Brady will undergo urgent surgery next week after doctors discovered she has an aneurysm on her brain.
A club spokesman said the 36-year-old managing director had been off sick over the past fortnight and her condition was diagnosed following a series of tests.
Ms Brady is due to have a lengthy operation at a hospital in London on Monday and is expected to take a month off before returning to the Premiership club.
Yesterday she told the club's website: "Obviously this has come as a big shock to me and my family, but I am in very capable hands, and diagnosing the condition this early is very encouraging.
"I would like to thank everybody for their messages of support and I plan to be back at work as soon as I possibly can."
An aneurysm is an abnormal swelling of an artery caused by the pressure of blood flowing through a weakened area, causing it to "balloon".
The condition is rarely diagnosed before an aneurysm ruptures, often leading to emergency surgery, but it is thought up to five per cent of people in Britain are unaware they have this condition.
David Gold, the club's coowner, said he was shocked by the executive's diagnosis.
"Karren called me this morning and in a very matter-of-fact way told me what had happened, that she was going to have an operation and was going to take a month off to recover," he said.
"Just a few months ago our financial director Roger Bannister was rushed to hospital after an aneurysm burst close to his brain, but he's now back at work and raring to go. I sincerely hope she will recover from this with the same success."
Surgeons at the unnamed London hospital where Ms Brady will have her operation could perform one of two procedures which stem the bloodflow to the swelling.
Margaret Garbett, clinical nurse co-ordinator for neurosciences at the Queen Elizabeth Hospital, in Edgbaston, said: "The first operation would involve opening up her skull to locate and 'clip' the aneurysm by blocking the blood supply to it.
"This is a very big operation as it can take between four and eight hours.
"A second, newer 'coiling' procedure involves feeding a catheter up through the groin, into one of the main arteries up to the brain and filling the aneurysm with very tiny coils - again to divert blood away from the swelling.
"There is a significant risk in both operations, because you are interfering with the blood supply to the brain which could lead to the aneurysm bursting or a stroke."
Professor Michael Frenneaux, a cardiology expert at Birmingham University, said aneurysms can remain latent for years before symptoms become apparent.
He added: "Aneurysms of all types can affect people at any age, often they are not diagnosed until after they've burst and people can suffer severe headaches and speech problems, similar to the after effects of a stroke.
"Changes in blood pressure maybe a factor, maybe as a result of increased stress, causing the aneurysm to swell. However if they are caught early, before the aneurysm ruptures, surgical intervention can produce very good results."
Ms Brady joined Birmingham City in 1993, aged 23, to become managing director when the club was struggling in the old Division One.
She is married to former Blues footballer Paul Peschisolido, who now plays for Derby County. They have two children, nine-year-old Sophie and Paolo, aged seven.
The club's commercial director Perry Deakin and financial director, Roger Bannister, will jointly assume her duties during her absence. ..SUPL: