Victory over Spain at Lansdowne Road would book Ireland's place in the finals in the United States; defeat would leave them with quite a bit still to do. Although Spain have packed their squad with central defenders, Charlton is alert to their counter-attacking qualities and needs McGrath for sentry duty.
McGrath missed last month's victory over Lithuania through suspension and by recalling him to the midfield, Charlton would leave undisturbed the defensive partnership of 37-year-old Kevin Moran, who is likely to be named as captain, and Alan Kernaghan. 'Andy is a difficult one to replace but we will manage,' Charlton said without excessive concern. John Aldridge is easing his way through training in the hope of recovering from a thigh strain.
Qualification would lead to wild celebrations here, on a scale the city has rarely seen before. When the victorious moments came in the 1988 European Championships and the 1990 World Cup, they happened on foreign soil.
Defeat for the Republic would make Spain favourites to qualify from Group Three and almost certainly leave Charlton's side needing to win in Belfast next month, a prospect they would not relish.
It is therefore imperative that the five players one yellow card away from suspension use their heads as well as their hearts tomorrow. Roy Keane will be shadowed by 'Chapi' Ferrer, recognised as the best marker in Spain, and knows he is vulnerable. 'I know Spain might try to get some of us sent off and I will just have to count to 10 even though I don't often get further than one,' Keane said.Reuse content