The front cover sketch shows the Hippogriff, an eagle-horse hybrid
Original Harry Potter book illustrations are to go on sale at the 14th annual Glasgow Art Fair.
The preparatory drawings by illustrator Cliff Wright were used as the basis for the front and back cover of Harry Potter and the Prisoner of Azkaban.
One drawing depicting Harry and his friend Hermione astride a "Hippogriff" - a hybrid of an eagle and a horse - will be on sale at just under £13,000.
The other sketch shows "the Grim" - a dog-like omen of doom.
It is priced at just under £11,000.
Drawn in pen and pencil on paper, the sketches will be on sale at the Art Fair in Glasgow's George Square from Thursday until Sunday.
Discussing the front cover, illustrator Cliff Wright said: "The image is one of a series of 10 which were sent to the publisher Bloomsbury as rough ideas for character development and composition."
The Grim is an omen of doom in Harry Potter and the Prisoner of Azkaban
The Hippogriff creature became a recurring feature of the Harry Potter series.
Mr Wright added: "The designs were also passed on to JK Rowling for her approval and any comments passed back to me. Thus, for example, the Hippogriff was based on a design that was sent through to me from Jo.
"Along with griffins and dragons, Hippogriffs can be found in medieval bestiaries."
Published in 1999, Harry Potter and the Prisoner of Azkaban was the third in the series of seven books and told the story of Harry's encounters with his mysterious godfather, a convict named Sirius Black.