She said: "The number is not known at all. There will be natural wastage and redeployment of staff across Gensler worldwide."
The spokesperson also said the company hoped to cut the number of jobs by voluntary means.
A 30-day consultation process over the proposed redundancies began on Tuesday.
These are not the first redundancies at Gensler's London office in recent times. Earlier this year, an undisclosed number of staff, reportedly 20, lost their jobs.
Gensler's recovery plan is based on the firm expanding its work in office interiors, retail design and masterplanning.