John Reid will climb into the seat vacated by Frankie Dettori when Seazun tackles the Sagitta 1000 Guineas at Newmarket on Sunday week.
Reid, 44, has won the fillies' Classic twice previously aboard On The House and Las Meninas.
"John's a top man and has ridden good winners for me, I'm delighted to get him," said Seazun's trainer Mick Channon.
"I've had to sort something out quickly for my horses as plenty of the other top jockeys are not going to be available."
Dettori partnered Seazun when she was runner-up to Petrushka in the Nell Gwyn Stakes at Newmarket last week.
But the Italian is riding China Visit in the Kentucky Derby on Saturday week and if he is back in time for the 1000 Guineas will probably partner Godolphin's Bintalreef.
Richard Quinn was the regular rider of Seazun last season, when her wins included the Cheveley Park Stakes, but he is now Henry Cecil's retained jockey and likely to ride his boss's High Walden in the 1000 Guineas.
Reid's agent Ian Shoemark said: "John's ridden a few winners for Mick when he's been available. A few years back he had a Group One win for him when Piccolo was awarded the Nunthorpe Stakes.
"Seazun is a great ride to pick up. She's a Group One winner and has an excellent turn of foot.
"She was beaten by Petrushka but was trying to give 3lb and the winner got first run. Also Mick said his filly would improve a lot for the outing.
"John hasn't sat on Seazun yet but there's a possibility he will go over to Mick's to ride her in work on Saturday."
Channon himself is refusing to believe that the 1000 Guineas is all over bar the shouting for the hot-favourite Petrushka.
Sir Michael Stoute's filly was most impressive when defeating Seazun last week.
But Channon insists that Seazun will not go down without a fight.
"The way some people talk you would think all the other Guineas runners were wasting their time," he said.
"They almost seem to think that Petrushka is already past the post. I'm not going to say any more now I'm just going to let my filly do the talking."
Channon is also planning to run Miletrian, fourth in the Prix Marcel Boussac, in the 1000 Guineas. She will be ridden by Michael Roberts.
Areydha, down the field behind Misraah at Newmarket last week, remains a possible third Channon runner in the 1000 Guineas, though she could be switched to the German equivalent.
"Whether she runs at Newmarket or in Germany she will be Steven Drowne's ride," said Channon.
"Not much should be read into her run at Newmarket last week as she experienced problems at the start."
