His mount, Sigma Run, fell two strides after the second-last flight of hurdles when in third place. Williamson was thrown under the plastic running rails on the inside of the track, but eventually got to his feet and limped into one of the course doctor's cars to be brought back to the weighing room.
The Irishman gave up his mount on Mini Cruise in the last race but expects to be fit to ride at Ascot today.
Tony Dobbin was not so lucky and will be unable to partner General Pershing in Saturday's big event at Aintree. Dobbin was hurt in a fall at Kelso on Monday, sustaining suspected crushed vertebrae, and leaves Gordon Richards without a jockey for his charge. "We're not sure who will ride General Pershing," Richards' wife, Joanie, said. "Gordon will have to do a bit of homework."
Similar work may have to be carried out by Josh Gifford on behalf of Topsham Bay and Jumbeau, because his stable jockey, Philip Hide, is suffering from a virus.
"We thought he had German measles but it isn't that and he's going to have to improve in the next 48 hours if he's going to ride in the National," Gifford said. "I've got Peter Hobbs and Simon McNeill in mind but haven't made any decisions."Reuse content