Fox was unseated after his mount, Luxford, veered sharply to the right.
Television replays showed the filly had been distracted by a stray golf ball on the course, which appeared to be thrown up by eventual winner Big Lachie.
The ball ricocheted off the helmet of another rider and across the sightline of Fox's mount.
Sandown Park in Surrey has three nine-hole golf courses close to the racetrack, but clerk of the course Andrew Cooper said they were not open on racedays.
"I am satisfied that we take all reasonable precautions to make sure that the course is as clear as we can make it but we accept that there will be some balls buried in the grass," said Cooper.
"We have a 14-strong team that walk the course, and other parts of the track, looking for golf balls.
"Even where there is netting next to the driving range we have found them. It is not a unique occurrence and we probably have this happen once every three or four years."
The afternoon ended on a more positive note for Fox as he partnered First Experience to victory.
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The former England international, who switched his allegiance to The Elephants ahead of their Nations Cup defence, came off the bench in Abu Dhabi to provide the perfect cross for Giovanni Sio who headed home a winner.
An own-goal from Wilfried Kanon had put Sweden ahead, with Yao Serge Nguessan equalising on the stroke of half-time.
24-year-old Zaha was born in Ivory Coast but has two England caps having played against Sweden in November 2012 and Scotland the following year.
As both were friendly matches, he was permitted to commit his international future to his country of birth.
The Ivorians have been preparing for the Nations Cup in the United Arab Emirates.
They will be heading to Gabon on Thursday and will play their opening Group C game on 16 January against Togo.
In other friendly internationals this weekend, Algeria were 3-1 winners over Mauritania; Burkina Faso beat Mali 2-1; Uganda defeated Slovakia 3-1; Senegal were 2-1 winners over Libya and Egypt recorded a rare victory over North African rivals Tunisia, winning 1-0.

The other contestants to have been announced so far are; Peter Andre, Carol Kirkwood, Katie Derham, Georgia May Foote, Kellie Bright, Ainsley Harriott and Jeremy Vine. More are still to be announced.
Mr O'Donnell said that he is nervous, despite his many years in show-business.
"It's really happening," he said.
The singer said he is uncertain if he is up to the standard required.
"I can put a few steps together, but can I dance to the level I need to dance? Well, that's a whole other ball game."
Earlier this year, the Kincasslagh man decided to take a short break from touring.
"I told myself that I would only consider doing something if it was both different and exciting. Well, what could be more exciting than Strictly Come Dancing? I love to dance and boy am I looking forward to getting started and being the best that I can be," he added.
Daniel O'Donnell, who has sold more than 15m albums, first rose to fame in 1983 and has had considerable success in Ireland, the UK, the US and Australia.
Strictly Come Dancing returns to BBC One for its 13th series in September 2015.
Jockey Kieren Fox escaped unhurt when he fell from his horse in a bizarre incident involving a golf ball during a race at Sandown.
[NEXT_CONCEPT]
Crystal Palace winger Wilfried Zaha provided the decisive cross on his Ivory Coast debut as the African champions beat Sweden 2-1 in an Africa Cup of Nations warm-up match on Sunday.
[NEXT_CONCEPT]
Irish singer Daniel O'Donnell has been confirmed as the eighth contestant on this year's Strictly Come Dancing.