The Irishman started the day on the 98-winner mark but had to surrender his bookings for Wise Approach and Mariner's Air after bruising his left leg in a fall from Gorby's Myth in Nottingham's second race.
Williamson reported himself "shaken and sore" after being thrown to the ground at the second-last flight of the Trowell Novice Hurdle.
Kim Bailey's stable jockey is hoping he will pass a medical examination this morning to enable him to resume riding at Towcester.
Adrian Maguire also missed most of the same meeting after a fall from Sparrow Hall in the third race. He, too, expects to be back in the saddle this afternoon.
n The weather yesterday claimed its first victim of the new turf Flat season. Today's card at Newcastle was abandoned after snow covered the track. Clerk of the course James Hutchinson said: "The forecast is for more snow and a heavy frost overnight. I can't remember ever calling off a Flat meeting due to snow but I believe my predecessor at Ripon, Freddie Newton, once had to do so in April."Reuse content