However, the 73-year-old, who won a previous battle with the disease, was said to be in a jovial mood following the significant weekend operation, believed to be linked to lung cancer.
“He was laughing and joking with nursing staff following the procedure,” a source said.
Staff at the Freeman Hospital in Newcastle were under strict orders not to discuss Mr Robson’s condition and would not officially confirm that he was a patient there last night.
It is also understood he is being treated under the National Health Service public health system, indicating he did not use his fame and local popularity to jump the waiting lists at the hospital known globally for specialising in lung transplants.
Mr Robson is a former Newcastle United manager and considered a football hero in the north east of England.
Having joined the Republic of Ireland’s senior international backroom staff when Steve Staunton was appointed manager in January, he is unlikely to join the squad’s training camp in Portugal next month.
Last night, an FAI spokesman said he had been scheduled to have what he described as a ‘minor lung operation’ on Saturday. But informed sources in Newcastle suggest the matter may be more serious.
Mr Staunton recently announced he would be bringing the Irish squad to the Algarve for a four-day warm weather training camp ahead of Ireland’s next game, a friendly against Chile at Lansdowne Road on May 24.
He described it as a key part of the squad’s long- term planning for the European Championship qualifiers which begin away to Germany in September.
As Mr Staunton’s most experienced adviser, Mr Robson would have been expected to attend the training camp which begins on May 20 but FAI sources say that his recuperation from the operation will take a number of weeks and it is therefore “highly unlikely” that he will be able to fly to the Algarve.