By John Kenny in London

Grainne Murphy has withdrawn from the heats of the women’s 400m individual medley at London 2012 on Saturday.

Her withdrawal leaves Barry Murphy as Ireland's sole competitor on the opening day of competition at the Aquatic Centre in London. He will swim in the heats of the men's 100m breaststroke.

According to Peter Banks, Swim Ireland's national swimming director, it was decided at this morning's technical meeting here in London that the Limerick-based teenager would concentrate fully on the freestyle events.

This means her first event will be the women's 400m freestyle. The heats of which are on Sunday morning.

Grainne is also down to compete in the heats of the women's 200m freestyle on Monday.

It was felt that it would be asking too much for her to compete in three tough events in three days, as she looks forward to her main event, the women's 800m freestyle, which takes place a week from today.

The final preparations for the opening day of competition in the impressive Aquatic Centre continue with the men's 400m IM the big event on day one.

That event features the big American matchup between defending champion Michael Phelps and Ryan Lochte, who beat 16-time Olympic medallist Phelps in the recent US trials.