Timmy Murphy is recovering at home after damaging two vertebrae in a fall at Newbury on Friday.
Murphy was partnering Leeroar in the closing Inkerman London "National Hunt" Maiden Hurdle when the duo fell at the third flight, and was subsequently taken for X-rays in Swindon.
His agent Chris Broad said: "He was released from hospital last night and has damaged two vertebrae.
"They are not fractured or cracked and they are stable.
"The prognosis last night was that he would be out for approximately six weeks. Dr (Philip) Pritchard was with him and advising him."
Murphy was due to ride The Package in this afternoon's Hennessy Gold Cup but Tom Scudamore will now be on board.
Trainer David Pipe tweeted: "Following Timmy Murphy's injury, Tom Scudamore goes to @RacesNewbury to ride my three runners - Star Of Angels, The Package and Consigliere."