Racing: Silk's tangle in National ends in cracked rib: The leading hunter chaser is knocked off course as the jumpers prepare for the last major chase of the season

A CASUALTY finally emerged yesterday from the muddy mayhem of the Grand National. After a week of X-ray examinations and tests, Double Silk, the country's leading hunter chaser, has been diagnosed as having cracked a rib at Aintree. He will miss the rest of the season.

Double Silk fell at the 13th, but continued riderless and sustained his injury two fences later, at the Chair. Reg Wilkins's gelding jumped the obstacle well, but landed on top of Black Humour, who did not. The tangle of legs which ensued was one of the race's most disturbing moments.

'I've cracked my ribs over the years and it's quite a painful thing,' Wilkins said yesterday. 'The vets have given him antibiotics to keep down any infection, but there's not much else they can do. But if everything goes all right he should be fine in a couple of months.'

The fence at which Double Silk parted company with Ron Treloggen does not possess the notoriety of Becher's or The Chair. This year, though, it was the most significant in the race, claiming the well-backed Master Oats and three other runners in addition to Double Silk, who had jumped the previous 12 fences brilliantly. Although he was was probably also distracted by a loose horse, Wilkins places much of the blame for his runner's mishap on the particuarly heavy going at that point on the course.

'He jumped that fence perfectly all right last year (in the Foxhunters'),' he said, 'but this year the going there was desperate, and it was jumping about six or eight inches higher than it looked.'

Even if the course had been under six inches of water, though, the Aintree executive would probably have issued each runner with flippers. 'I don't think I've seen much heavier, and the hailstorm in the morning didn't help,' the trainer said. 'But I suppose with the fiasco there the year before they really had to run. We made contact on the way up to find out if they were going to run and they were definitely going to, in anything.'

Another National runner whose race ended at the 13th was Topsham Bay. David Barons's gelding was uninjured, however, and will return to action at Sandown on Saturday, when he will attempt to win the Whitbread Gold Cup for the third year in succession.

He is not strongly fancied to do so. Antonin, winner of his last three races including the Racing Post Chase, is shoulder-to-shoulder with Flashing Steel, fourth in the Gold Cup, at the head of the market, while Docklands Express, winner of the race in 1991, and Young Hustler are also preferred to Topsham Bay in the early betting.

'He's in great form,' Sue Bramall, Antonin's trainer, said yesterday. 'The soft ground should suit him very well, and even if it went to good that would not be a problem.'

The principal supporting race on Sandown's excellent mixed card is the Thresher Classic Trial, the first Derby trial of the season. The race, once a regular proving ground for Epsom winners, has lost some of its significance in recent years, but 13 of the 16 entries at yesterday's five-day stage are at least engaged in the premier Classic.

The most interesting of those is probably The Deep, who was thought worthy of a supplementary Derby entry, at a cost of pounds 10,000, by Barry Hills, his trainer. Overbury (trained by David Loder), Khamaseen (John Dunlop), Linney Head (John Gosden) and Ionio (Clive Brittain) are also expected to run.

The Derby could yet be the first domestic Classic in which Lanfranco Dettori, the season's top Flat jockey, manages to find employment. Dettori has yet to be booked for either of next week's Guineas races at Newmarket, though Grand Lodge and Mister Bailey's are still available in the 2,000 Guineas on Saturday week.

Dettori's name had also been mentioned in connection with Bulaxie, second-favourite for the 1,000 Guineas. Yesterday though the mutterings suggested that Michael Kinane, the Irish champion, will ride John Dunlop's filly at Newmarket on 28 April. Exprect an avalanche of cash to follow if the booking is confirmed.