British medal hopes were dealt a knock on Tuesday night by the withdrawal of William Fox-Pitt and Tamarillo from the three-day event competition.
The injury to the horse's stifle - the equivalent of the human knee - scuppers Team GB's hopes of landing a medal from a competition they were expected to impress in.
It completed a near-disastrous day for the British side, who started the day in gold medal position in the team event and ended it in fourth.
News of Tamarillo's injury followed on from a disappointing show from Pippa Funnell on Primmore's Pride, who finished almost 30 seconds below the optimum time in the cross-country phase and dropped from second to eighth in the individual standings.
A statement from the British Olympic Association read: "Following the withdrawal of William Fox-Pitt and Tamarillo from the eventing competition of the Olympic Games, Team GB have announced that during the cross-country phase of the competition, Tamarillo sustained a slight injury which - following an investigation - will prevent him being presented for the final veterinary inspection prior to the showjumping phase.
"The injury is not serious but horse welfare is always a prime consideration. Tamarillo suffered a knock to the stifle which will prevent it showjumping."
As well as being an individual blow to Fox-Pitt, the news damages Team GB's hopes of success.
After starting the day with a realistic chance of winning three medals, Britain were relying on Fox-Pitt - who was lying fifth in the individual event - to hold off the challenge of the US, who are only four points adrift, in the showjumping phase just to clinch a bronze.
The Briton had gone out late and recorded one of the clear rounds to leave him just three points behind Germany's Bettina Hoy, who sits in the silver medal slot.
The gold already appears to be heading to France as Nicolas Touzaint managed to avoid adding any penalties to the 29.40 that put him in front after the dressage phase. The French have also established a clear lead in the team competition, and although Britain have a chance of equalling their second-placed finish in Sydney four years ago, the loss of Fox-Pitt makes it harder for them to close the six-point gap by which they trail Germany.
Mary King now becomes part of the scoring British team - as the top three riders only count towards the team event.
GB team leader Will Connell said: "Of course the whole team are extremely upset for William, Tamarillo and the owners of the horse.
"William had an outstanding result when riding at Badminton this year and this is a very unfortunate way to end his Olympic campaign."