Deaten Registe and Barry McClements failed to progress from their respective heats on Day 3 of the Para Swimming World Championships in Shanghai.
In his 100m butterfly event, McClements swam a time of 1:03.29 and was left to rue a below-par performance.
"I'm not too happy with the race at all," he said. "I’m two seconds off my PB and not close enough to a final. It’s disappointing."
He will return to the pool on Friday for the S9 100m backstroke.
Later today Dearbhaile Brady will make her first appearance at this year’s world championships in the SM6 200m individual medley final.
