The General Medical Council is understood to be considering a move to Allied London's 3 Hardman Street in Spinningfields, Manchester.
The GMC has a 50,000 sq ft office requirement in the market and has made the 390,000 sq ft building the frontrunner ahead of Langtree's 40 Spring Gardens, Argent's Piccadilly Place and Wilson Bowden's Belvedere.
The doctors' regulator currently occupies Bruntwood's St James's Building on Oxford Road.
Bank of New York Mellon recently agreed to take 50,000 sq ft at 3 Hardman Street, following deals to law firm Pinsent Masons and serviced office provider Regus.
BDO Stoy Hayward and PricewaterhouseCoopers are also interested in the Allied building. Completion is scheduled for the autumn.
Allied would pass the halfway-let mark if the GMC agrees to sign for 3 Hardman Street.
Meanwhile, Barclaycard is at last likely to take part of its 80,000 sq ft pre-let at 3 Hardman Street which it threatened to pull out of in 2007.
The bank will fill half of the space and sub-let the remaining 40,000 sq ft.
Jones Lang LaSalle is retained by the GMC and is joint letting agent with DTZ on Spinningfields. Langtree is advised by CB Richard Ellis and WHR. JLL and WHR act for Wilson Bowden, and GVA Grimley and King Sturge represent Argent.