The final date for the invitations to tender for new project managers is 31 July.
Gary Philpot, administrative director for the Royal College of Art, confirmed that Mace had left the project management position after working on the project for most of the year.
He said: "The decision comes after long discussions from which it became clear that things were not going to work out. It was an amicable process and one of mutual consent."
The Nicholas Grimshaw & Partners-designed building will provide about 3000 m2 of space for teaching research and support services, and will form the main entrance to the college.
A planning application for the five-storey building is set to be submitted in October.
The services engineer is Atelier Ten, structural engineer is Buro Happold and the quantity surveyor is Davis Langdon & Everest.
Nicholas Grimshaw & Partners won the competition to design the block last July; it was picked from a shortlist of six.
The development has attracted controversy because of its proximity to the Royal Albert Hall.
