Willie Mullins has warned that new VAT costs arising from Brexit will have a major impact on Irish connections sending horses to the UK.
A VAT payment of 19% will have to be paid to the British Government when horses are sent to race in Britain from Ireland.
The tax will be refundable but Mullins points out that it could take months to recoup and warns that it could cause major issues for the Cheltenham Festival.
Mullins will send Champion Bumper hopeful Grangee to compete at Market Rasen tomorrow, and in doing so will become the first trainer to send a horse from Ireland to race in Britain post-Brexit.
"I'm told we have to pay 19% of her value in VAT and we mightn't get that back for three months so that would be a bit of a worry," Mullins told The Racing Post.
"The sums of money involved in bringing a big team of horses over, let's say to Cheltenham, could be colossal so there has to be a better mechanism in place for Cheltenham."
Cheltenham organisers Jockey Club Racecourses say they are working on a solution ahead of the Festival in two months' time.
"We are well aware of the current issues of bringing horses into the country from Ireland and are exploring ways to help to minimise the difficulties encountered by Irish owners and trainers," a spokesman said.
"This include working with the various authorities, including HRI, to seek to resolve financial burdens, including VAT costs."
