The £10m could exceed the annual turnover of the 16-partner City firm, which will defend itself against Ball's claims in the High Court this November.
The amount is also twice the sum he unsuccessfully sued multimillion-pound tourist attraction the Eden Project for two years ago, after he was sidelined from the project and removed as a director.
Ball, an architect, is accusing Druces of failing to advise him on how to protect his position in the project. In the claim, he also slams Druces for starting to act for the Eden Project and the Eden Project trust while he was a client.
Druces has already been banned from acting for the project and the trust by the High Court, which ruled that the firm's previous relationship with Ball created too much of a conflict. Druces had tried to represent Eden over Ball's claim against the project, despite its previous four-year relationship with the architect, and was ordered to pay £20,000 costs to Ball for failing to declare the conflict.
Toby Stroh, the partner who originally advised Ball on the Eden Project, is still working at Druces.
In this new claim, Ball is being advised by McDermott Will & Emery litigation partner Larry Cohen.
Druces is believed to be representing itself at the High Court, with litigation head Richard Sherrin handling the case. Sherrin declined to comment.