Leading bookmakers suspended betting on Saturday's Tattersalls Millions Irish Champion Stakes at Leopardstown due to a rush of money for New Approach.
The market was taken down by Ladbrokes as long-time ante-post favourite Duke Of Marmalade was friendless in the betting.
"We've suspended the betting on the Irish Champion, I think pretty much everybody has," said David Williams of Ladbrokes. "We took a good number of bets on New Approach this morning, more than we would have expected at this stage of the week.
"That might not necessarily mean anything but we just kept on laying only one horse so we thought 'hang on, let's just take a breather' so we suspended and we will wait for clarification to come from the respective camps and as soon as we do we will be back up and running."
Ladbrokes later decided to suspend their market until the declaration stage tomorrow morning.
"With the final declarations confirmed on Thursday lunchtime, we've decided it prudent to suspend the market until then," said Williams.
The betting exchange Betfair has also seen significant action in the market with Duke Of Marmalade drifting out to 3-1 before settling back around the 6-4 mark.
Betfair spokesman Tony Calvin commented: "It could well be a false move, and we are certainly not talking big sums here, but a drift to 3-1 is obviously worrying for his weekend supporters."
William Hill reopened their market at approximately 12.15pm having eased Duke Of Marmalade out to 4-5 from 1-2. Derby winner New Approach is now 11-10 from 2-1.
William Hill's Irish spokesman Tony Kenny said: "Between 9.00am and 9.30am this morning we took several four figure wagers on New Approach, and at that stage we decided it was everyone's interest to suspend the market.
"We're expecting a lot of rain in Dublin over the next few days, and if that expected downpour comes - then there could be doubts about the participation of Duke Of Marmalade.
"The Irish Champion Stakes looks like a match between Duke Of Marmalade and New Approach, and it would turn the market on its head if either of them was withdrawn."
The going at Leopardstown is described as good though they are forecast as much as 20 millimetres of rain on Friday.
"There are showers forecast later today and tomorrow and then there is some rain forecast early on Friday to reach Dublin at around dawn. That could persist during the day," said racecourse general manager Tom Burke.
"They are talking maybe 20mm but it's a bit uncertain.
"The forecast seems to be changing each day. The indication is we could get quite a bit of rain on Friday, but we are working on good ground at the moment."