Tidal Bay
(Healy Racing Photos)

The enigmatic 12-year-old has returned to his brilliant best this season, winning a thrilling renewal of the Lexus Chase over Christmas, and had been allotted what looked a favourable handicap mark for the Aintree spectacular.

However, Nicholls confirmed on his blog at www.betfair.com/paulnicholls that a minor injury has been discovered.

"He was out cantering as usual on Monday and Tuesday, but on Wednesday we decided to step up his work," said the Ditcheat trainer.

"But his work rider came back up and said he didn't feel right.

"So we immediately called in Buffy and, after discussions, we got him down to Newmarket today for an MRI Scan.

"The news through from Buffy is that Tidal Bay has a tiny stress fracture of the lower cannon bone on his right hind leg.

"This is something that the X-rays we took before his problem in the Argento didn't pick up; only today's MRI did.

"He needs a month's box rest, so that rules out the National."