Harry Cobden will replace Harry Skelton aboard Politologue in the Grade 1 Matchbook Exchange Clarence House Chase at Ascot on Saturday and is also set to partner the grey in the Champion Chase at Cheltenham in March.
Skelton rode the Paul Nicholls-trained Politologue to victory in last season's Champion Chase and was in the saddle again when the ten-year-old took the Tingle Creek at Sandown in December.
However, his role as stable jockey to his brother Dan means he is likely to be aboard Desert Orchid Chase winner Nube Negra in the Champion Chase.
"It's unfortunate circumstances," Harry Skelton said. "The owners [John and Lisa Hales] wanted whoever rode him on Saturday to ride him in the Champion Chase. But if Dan's horse makes it to the festival then, as his stable jockey, it is my job to ride him."
Nube Negra emerged as a legitimate Champion Chase contender after getting the better of Altior at Kempton last month, and is fourth in the Champion Chase market at a general 10-1.
Cobden has won two of his eight starts on Politologue but has not ridden the grey in a race since the pair were tailed off behind Defi Du Seuil in the 2019 Tingle Creek.
Politologue is the general 6-4 favourite to win a third consecutive Grade 1 at Ascot on Saturday, with King George runner-up Waiting Patiently next best at 5-2.