Have you any idea where the concept of John Watson having money problems from gambling originates?
Doing a REALLY quick google search, I found this on the Dr. Watson Wikipedia:
In the Guy Ritchie-directed Sherlock Holmes movies, Watson is portrayed by Jude Law. Law portrays Watson as knowledgeable, brave, strong-willed, and thoroughly professional, as well as a competent detective in his own right. Apart from being armed with his trademark sidearm, his film incarnation is also a capable swordsman. The film portrays Watson as having a gambling problem, which William S. Baring-Gould had inferred from a reference in "The Adventure of the Dancing Men" to Holmes keeping Watson's cheque book locked in a drawer in his desk.[18]
Obviously, Wikipedia isn’t the BEST resource, but I’ll take it for now :) I honestly thought it was an ACD thing and was more blatant than one single line, heh.