In a deleted scene for "Harry Potter and the Chamber of Secrets" film, Harry (hidden in the Vanishing Cabinet?) observes Draco Malfoy and Lucius Malfoy going to Borgin and Burke's shop, and Malfoy informing Borgin that he is there to sell, not to buy items, due to raids by the Ministry. So far, close to the book.
Then, in a scene where the book has Malfoy giving Borgin a parchment with a list of items he wishes to sell, the movie's deleted scene instead has him put down a big box full of items, and Borgin examines them one by one.
In the middle, Borgin picks up an item, and Lucius forcefully tells him "This particular item... is NOT for sale!". Borgin then replies "I... I understand... It has unique qualities. One wouldn't want to see it fall into the wrong hands".
However, the scene is quite dark and murky and focus is on their faces. So it's entirely unclear which item Lucius refused to sell.
Is there any canon info on what that item was? (including movie canon).
My best guess would be that it was implied to have been Tom Riddle's Diary, but I am at a loss to find any evidence confirming that.