Sir Bobby Robson will undergo surgery to remove a brain tumour this week.
The former England and Newcastle manager, 73, fell ill during a match at Ipswich, the club he managed for 13 years and who have now made him president, a fortnight ago.
It was initially thought that Robson had suffered a stroke but doctors have discovered a tumour.
Robson, who has overcome cancer three times in the past, told the Mail On Sunday: 'I had a scan to assess why I felt unwell and had to leave the game at Ipswich early, and the doctors discovered a small, operable tumour that caused an affliction on the left side of my face.
'On Wednesday I will have an operation to remove the tumour and, as surgeons tell me the rest of my body is clean, I should be able to make a full recovery.
'The tumour is in my brain, which sounds bad, but it is in a position where it can be removed relatively easily and it's extremely small - the size of a grape - which indicates they have caught it early.'
Robson will naturally be unavailable for Ireland's opening Euro 2008 qualifier against Germany in Stuttgart on September 2.
But the Football Association of Ireland are hopeful he will be able to resume his duties alongside manager Steve Staunton for the games against Cyprus and the Czech Republic in early October.
An FAI spokesperson said: 'It's unfortunate that Sir Bobby won't make it to Germany.
'Our next match is on October 7 away to Cyprus and obviously the situation will be clearer following Bobby's surgery, which we all hope will be a complete success.'