THE top three clubs in the Insurance Corporation All-Ireland League First Division all have problems through injury and illness as they prepare for a crucial series of matches. Nor are the problems confined to the leaders, for their immediate pursuers have similar difficulties.

St Mary's College, who lost the league leadership to Lansdowne and their unbeaten record in the competition in their last engagement, will be without their captain, prop forward Brian Keane, for the visit to Ballymena on Saturday. Keane is out with a viral infection. They switch Emmet Byrne from tight to loose head in the absence of Keane, and bring in under-21 Peter Coyle on the tight side.

Their experienced open side flanker, Kevin Devlin, is not available, and Mark Reilly is dropped. That means a revision of the back five: Dan Bourke goes into the second row, Kevin Potts switches to the blind side flank, Victor Costello is at number eight and Mark Cuddihy is on the open flank.

Ballymena have recalled half backs Ricky McIlmoyle and Mark Beattie for Gareth Harran and John Law, who played in the team beaten by Cork Constitution in the last league engagement.

Lansdowne, who lead the division on points difference from the defending champions Shannon, and the Limerick side themselves must wait until later in the week before being sure of their line-ups.

Lansdowne have named Eric Elwood in their side to make the hazardous trip to Young Munster, but Elwood is under treatment for a knee ligament injury and his chances of playing seem remote. They can move Ireland under-21 outside-half Richard Governey from full back to fill the number 10 spot, but are keeping their options open. Former Ireland centre Brian Glennon is fit again and he could play at outside-half, or they could move Kurt McQuilkin from centre to outside-half and bring in Glennon to centre. But Governey at outside-half seems the most likely option.

Lansdowne, who will have their international scrum-half David O'Mahony back following a bout of influenza, face an unchanged Young Munster line-up from the side that defeated Terenure College in the last league engagement.

Shannon, who travel to Old Wesley, are waiting on the fitness of international forwards Mick Galwey (back) and Eddie Halvey (ankle). Wing Billy O'Shea is also under treatment, while there is some doubt about prop Donal Costello because of a family bereavement. Old Wesley hope that backs Colin Younger and Rory Moroney will be fit after missing the last league engagement, while forwards Richard Jackson and John Quirke are also under treatment.

Garryowen have also deferred selection and await fitness reports on Ireland A centre Killian Keane, Ireland A second row Shane Leahy and international number eight Ben Cronin before finalising their side to entertain Cork Constitution. With centre Brian Walsh ruled out, Constitution will probably field the same back division that played against Ballymena. But international Paul McCarthy will be a contender for a prop berth and Don Lynch could be available in the second row.

Former Ireland schools international Cillian de Gascun is among nine backs in the panel from which Terenure College will finalise their line-up for the home match against Dungannon. The pack will be unchanged. Dungannon have Stanley McDowell and Keith McGarry back after long absences. McDowell plays in the centre and McGarry at outside-half. McDowell comes in for the injured Ricky Stevens, and McGarry for Ashley Blair. In the pack, Willie Dunne returns on the flank for Michel Beggs.

Instonians, who won their first league match of the season last Saturday week against Old Wesley, will be unchanged for the visit to Old Belvedere. Barry Murphy returns at scrum-half for Old Belvedere, Lars Weigand takes over at hooker from Paddy Kenny and Mark Feely resumes in the second row. But Kevin Spicer is out with a hamstring injury so Hugh McDonnell moves to the back row, where Fergal O'Beirne also comes in for David Shanley.

Brian Carey is fit again after being injured playing for Ireland A and plays at full back for Blackrock College against Old Crescent. He takes over from David Beggy, who has been hit by a hamstring strain. Emmet Farrell again keeps Alan McGowan out of the outside-half berth and Dean Oswald, who has yet to play a league match, has been chosen on the flank, but his return could have to wait another week or two. Old Crescent will have Len Dinneen back in their pack, but are likely to be without second row Daragh Kirby. They will not finalise their team until late in the week.