Bethany Firth has withdrawn from the SB14 100m breaststroke heats on Thursday because of a shoulder injury.
The 16-year-old from Seaforde aggravated the injury when she clinched the gold medal in the S14 100m backstroke last Friday night.
The shoulder problem also kept the teenager out of the 200m freestyle heats at the Aquatics Centre on Monday.
She is Northern Northern Ireland's youngest Paralympian and took up swimming just three years ago.
Firth led after 50 metres in the backstroke final and went on to win in a personal best time of 1:08.93.
She struggled with shoulder injuries before the Games but was fit enough to make her Paralympics debut.
The schoolgirl claimed silver in the 200m freestyle at the European Championships last year.