Tiger Roll has been ruled out until February at the earliest as the two-time Grand National winner needs a chip removed from a joint.
The four-time Cheltenham Festival winner must be considered a doubt for the 2020 edition at Prestbury Park, despite connections' confidence the 9-year old will be fit by then.
The small chip was due to be removed from a joint on Friday, with Gigginstown racing manager Eddie O'Leary feeling the best-case scenario is Tiger Roll returning in the Boyne Hurdle at Navan in February.
Trainer Gordon Elliott previously said he wants Tiger Roll to attempt a hat-trick of Grand National wins, a feat only ever achieved by Red Rum.
Gigginstown manager Eddie O'Leary said of Tiger Roll's chip, "It’s more than a little bit of a setback, you can’t be a little bit pregnant, it’s a setback, unfortunately."
"He’s a very sound horse, he exercised on Tuesday perfect and on Wednesday the problem was diagnosed."
Elliott backed the plan to have Tiger Roll return at Navan, "It is obviously not ideal and I would have preferred if it didn't happen, but I would hope to have him back for the Boyne Hurdle and then on to Cheltenham all being well. That is what we are hoping for."
O'Leary fleshed out the details, adding, "He’s being operated on and hopefully they can suck it out.
"He should be back for Navan and the Boyne Hurdle in February after being in his box three or four weeks.
"We just need to get him sound before making plans."
Gigginstown owner Michael O'Leary recently rated Tiger Roll's chances of attempting the Aintree hat-trick as "slim and none", unrelated to this setback.
The RyanAir boss told the Racing Post, "Now, does he run around Aintree well? Yes, he does. Is he going to carry 11st 10lb in a Grand National, with Gold Cup seconds and thirds getting six or eight pounds off him? No, he is not."