Horse racing at Doncaster Racecourse has been cancelled today due to an outbreak of equine flu.
Henderson's leading hopes for the Festival include champion hurdler Buveur D'Air and champion chaser Altior.
The BHA said on Thursday that its veterinary team "has been in contact with more than 50 trainers and veterinarians to allow it to make an informed assessment of the risk of equine influenza spreading".
Since the incubation period for equine influenza can be up to 72 hours, samples will be taken on Friday from horses that raced at Ayr and Ludlow and sent to the Animal Health Trust in Newmarket for analysis.
How has the situation unfolded?
All race meetings in Britain have been cancelled until next Wednesday at the earliest while the sport's governing body awaits test results from more than 100 horses which could have been exposed to equine influenza.
The BHA issued a warning to racing professionals on January 19 but, until now, no cases in Britain had been confirmed from active yards in vaccinated horses. Racing is continuing as normal in the Republic of Ireland.
He said: "We're making preparations for alternative arrangements - so that when racing returns, if there were prep races for horses going to Cheltenham or Aintree, they'll have alternative races in place".
"It is very, very virulent so it does not matter how much pains you go through to keep these things at bay, it is very unsafe".
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"We are all totally vaccinated - rigidly, it's compulsory".
The decision that British horses should be barred from entering Irish races was deemed "a prudent step in the short term" by the IHRB's Dr Lynn Hillyer as the risk to disease in Irish thoroughbreds was unchanged.
It is too early to say "definitively" whether the four-day Festival, due to start on 12 March, will go ahead, said BHA chief executive Nick Rust.
Only two events have cancelled the Cheltenham Festival in the past; the 2001 foot-and-mouth crisis, and the second World War.
"I don't know if that will need a few more days or not".
The British Horseracing Authority is confident its prompt action and "war-room" of vets can stop equine flu shutting the sport down for months.
"When the email came through at 11.30pm (on Wednesday) from the BHA it sent shockwaves through the industry".
Speaking to BBC Scotland, she added: "I'm disappointed for the people who were coming to see these wonderful horses and who might not get a chance to see them at Cheltenham or just on TV".
"It was probably the right thing to do by the BHA and a clean thing to do instead of saying to a whole lot of trainers "you can't run or move your horses".