The Financial Times reported on Tuesday that up to 14,000 of 18,000 jobs at RBS's investment bank could be cut, citing two people familiar with the matter.

"Until we've gone through and worked through the sale or rundown of these businesses, and also had good consultation with our unions and our staff, there is no number," McEwan told Sky News on Tuesday.

However, McEwan acknowledged that the number would be significant and sources familiar with the matter confirmed to Reuters that thousands of jobs would be lost.

RBS is shrinking its investment banking operations dramatically, pulling out of 25 countries in Europe, Asia and the Middle East while cutting jobs at its U.S. trading business in Connecticut.

Its investment bank expanded dramatically under former CEO Fred Goodwin, culminating in the disastrous acquisition of ABN Amro in 2007, which nearly destroyed the bank prior to its 45 billion pound bailout.

McEwan, who took over as chief executive in 2013 from Goodwin's predecessor Stephen Hester, has refocused the bank on lending to British businesses and households.

Announcing the restructuring last week, he told reporters: "This marks the end of a standalone global investment bank model for RBS."

(Reporting by Matt Scuffham; Editing by David Goodman)