Explaining his decision, Pipe cited fears over the risk of the horse, Tanterani, picking up an infection in the sampling unit.
But having already been warned by the Jockey Club that failure to allow tests to be carried out in the unit would trigger the disciplinary process, Pipe has been asked to attend Shaftesbury Avenue headquarters.
The Jockey Club’s disciplinary department is liaising with Pipe’s legal advisor in a bid to resolve matters.
In essence, there are three options - firstly that the hearing goes ahead, secondly that it does so in Pipe’s absence, or thirdly that it is deferred to a later date.
“At the moment, we don’t know whether Wednesday’s hearing will be going ahead,” said Jockey Club spokesman Owen Byrne. “We’re working with Mr Pipe’s solicitor to try and get things sorted out as soon as possible.”
If Pipe is found guilty of deliberately refusing to follow the rules over dope-testing procedures, he faces a fine of upwards of £2,500.
Meanwhile, Venn Ottery, who holds lofty entries at Cheltenham and Aintree, could have his first run for Pipe at Newbury on Saturday.
He is among 24 horses in the £100,000 Vodafone Gold Cup Handicap Chase over two and a half miles.
The 10-year-old, owned by Oliver Carter and formerly in his care, is in the Queen Mother Champion Chase, the totesport Cheltenham Gold Cup and the John Smith’s Grand National.
Pipe has also entered It Takes Time, winner of the totesport Chase at Lingfield recently, in the Newbury contest, as well as Horus, who was seventh to Farmer Jack in Saturday’s Racing Post Chase.
Jonjo O’Neill is double-handed at this stage with Knife Edge and Simply Gifted, while Nicky Henderson can choose from Chauvinist and Scots Grey.
Other interesting possibles include Francois Doumen’s First Gold, Buckby Lane from Paul Webber’s stable, the Henry Daly-trained Hand Inn Hand, who was third to It Takes Time at Lingfield, and Grand National winner Amberleigh House.
: 5-1 Buckby Lane, 7-1 Hand Inn Hand, It Takes Time, 8-1 Chauvinist, Claymore, 9-1 Le Duc, 10-1 First Gold, Mouseski, Supreme Prince, Whereareyounow, 12-1 Scots Grey, Venn Ottery, 14-1 Mister McGoldrick, 16-1 Turgeonev, 20-1 Knife Edge, Simply Gifted, 25-1 Horus, Korakor, 33-1 Avalanche, Marked Man, The Villager, 40-1 Amberleigh House, Jordans Lad.