The agency was one of five shortlisted by HSBC, along with BBDO, Grey, Saatchi & Saatchi and the incumbent, JWT.
Sources close to HSBC claimed the agency was asked to drop out because of recent changes to its management team.
It leaves McCann parent company IPG without a role in the contest, which is now between the two WPP shops, Omnicom and Publicis Groupe.
A McCann spokesperson said: "It was a mutual agreement with HSBC that we decided to pull out of the pitch. We’re in a pitch with another global bank."
The spokesperson denied the decision was related to IPG’s replacement of McCann Worldgroup chief executive Nick Brien with Harris Diamond last week.