The Prime Minister's good luck message to Andy Murray ahead of his quarter-final tie sparked concern among fans who fear the "curse of Cameron".
On previous occasions, sporting stars have seen their hopes of glory fade following a message of support from the Tory leader.
Bookmaker William Hill has launched a campaign to "BanCam" from issuing messages of encouragement.
A spokesman said: "A message of luck from David Cameron to British sports stars is like kryptonite to Superman. We are imploring the Prime Minister to instead send his messages to their opponents."