"I still don't quite know what happened; I'm in shock and disbelief. Even if I had recovered it would've been useless. I suppose that's sport; like a cyclist getting a puncture."
Trappitt, 26, had the support of 19-year-old Macfarlane in the media zone: "We're a team and we'll be supporting each other through this. We're looking forward to Rio from here."
There was better news for women's double scullers Fiona Paterson and Anna Reymer. They have suffered several illness related setbacks this year but came second to Great Britain in their heat. The result puts them straight into the final.
Paterson and Reymer took bronze at last year's world championships but could manage just two fifths at their 2012 World Cup regattas in Lucerne and Munich.
"It's been a rocky last four months having turns being ill," Paterson said. "We suffered a few bugs and fatigue but finally we're up for it together which is exciting."
Reymer said they were prepared to let the British win the heat.
"They're a bloody fast crew and we didn't want to get sucked in to killing ourselves."
The men's quadruple sculls won their repechage to go through to the semifinals. The men's coxless four finished fourth in their heat. They have a repechage tomorrow.