Trainers owed large sums in unpaid invoices by the Al Shaqab ownership group remain concerned about the outstanding sums, despite a formal assurance they are to be paid soon. British racing insiders spent the day reacting to a report the collective debts of the group amount to over £1m, with one saying he saw that as a conservative estimate.

A spokesman for the billionaire Qatari owners has admitted unspecified debts have been outstanding for months and offered a general apology to those affected. He insisted all sums would be paid in the near future, after the completion of what appears to have been a lengthy financial review.

However, the trainers who looked after the scores of horses that carried Al Shaqab’s colours last year have heard such promises before. “We have had previous assurances, along the lines of: ‘Yes, it’ll be fine, please bear with us.’ This latest one does appear to be a little bit more concrete,” one said.

Another of those involved claimed several trainers are now owed “significant six-figure sums”. He said: “There are not many businesses that could survive this kind of debt for any length of time and we are approaching the end of our tether.” One trainer has sent Al Shaqab’s horses back and will no longer train for the group.

Another said: “It’s an unfortunate situation that has put us all in some difficulty. Obviously there must be money. They’re one of the richest states in the world. I don’t know what the problem has been. I’ve had to ask my bank to extend the overdraft.”

However, not everyone has been made to wait. Two trainers reported Al Shaqab had paid them recently while Newbury, where Al Shaqab sponsors the Lockinge Stakes, said: “All of our commercial dealings have been satisfactory to us.”

The fact Al Shaqab should have caused such a crisis for those it deals with is astonishing and likely to be a source of embarrassment to Sheikh Joaan, a member of Qatar’s ruling al-Thani family and a brother of the Emir, particularly since part of the aim of Al Shaqab was to promote Qatar overseas. A source told the Guardian the problem had been “a middle-management cock-up” and expressed the hope Sheikh Joaan would now step in to sort it out, his attention having been occupied by Qatar’s diplomatic crisis. Several other countries in the region have severed relations and imposed a trade embargo.

That was specifically ruled out as a contributing factor to the debt problem by Khalifa al-Attiya, Al Shaqab’s general manager, said. “The blockade against Qatar had many consequences socially and politically but not for this situation,” he said. “This is purely an issue due to the financial review taking a longer then expected time.

“We do apologise and it is not something we wanted to happen or take lightly. We are in the middle of restructuring the whole organisation.” He said all invoices would be paid “in the coming weeks”.

While Al Shaqab have made themselves a difficult client for many, they are also valued as a rare source of top-class racehorses, just one of which might transform a trainer’s fortunes. For that reason most trainers are unwilling to end relations, even when their businesses have been undermined by slow payment. After only four years in the game Al Shaqab has owned the dual Arc winner Treve, the Guineas winner Galileo Gold and classy milers like Toronado and Olympic Glory.

The British Horseracing Authority said: “While we would not comment on speculation surrounding individual cases, more generally the rules allow for the BHA to mediate on any dispute over unpaid training fees when a complaint is raised to the BHA and where a training agreement exists between the owner and trainer.” But it is understoodno such complaint has been made about Al Shaqab.