"It would be naive of me not to think that there could be problems over player releases," he said. "But I am not going to go looking for those problems.
"My duty is to select the best players available but I am dependent on the good will of club managers.
"Because of the postponement of our European Championship game against Macedonia scheduled for Skopje last month, we have not played a match since 12 February. That makes the Swedish fixture all the more important in our preparation for the European Championship ties at home to Yugoslavia and Macedonia in June."
Alex Ferguson may not be keen to release Denis Irwin and Roy Keane with Manchester United still involved in the hunt for three major trophies.
The same applies to David O'Leary at Leeds who will want to retain Ian Harte as a vital part of his bid to win a place in Europe's elite next season.
The Wolves striker Robbie Keane, currently with the Republic's Under- 20 side at the World Cup finals in Nigeria, will almost certainly be required by his club as they attempt to reach the First Division play-offs.
Blackburn are likely to insist that Jason McAteer, Lee Carsley and Damien Duff stay at Ewood Park with Brian Kidd's men fighting to avoid relegation and the same argument could be applied in the cases of Mark Kinsella (Charlton) and Gary Breen (Coventry).
McCarthy, therefore, has named four players on stand-by: Dean Kiely of Bury, Bradford's Gareth Whalley, Wimbledon's Mark Kennedy and Steve Finnan of Fulham.
REPUBLIC OF IRELAND SQUAD (v Sweden, friendly, Lansdowne Road, Dublin, 28 April): Given (Newcastle), Kelly (Sheffield Utd), Irwin (Manchester Utd), Carr (Tottenham), Staunton (Liverpool), Harte (Leeds), Cunningham (Wimbledon), Breen (Coventry), Babb (Liverpool), Keane (Manchester Utd), McAteer (Blackburn), Kinsella (Charlton), McLoughlin (Portsmouth), Carsley (Blackburn), Duff (Blackburn), Quinn (Sunderland), Cascarino (Nancy), Keane (Wolves), O'Neill (Middlesbrough), Connolly (Wolves). Standby: Kiely (Bury), Whalley (Bradford), Kennedy (Wimbledon), Finnan (Fulham).