He handed in his resignation before Christmas after a new sales structure was proposed by Mike Gordon, who joined the company as group commercial director on 1 December.
Global Radio allowed him to leave immediately instead of working out a notice period.
No replacement has yet been found and it is unclear whether Global Radio intends to replace him.
Legg was Global Radio’s operations sales director before the group took over GCap Media. When the two companies merged, he was appointed business development director and led client and category development, as well as looking after a key set of agencies. He reported directly to Gordon.
A Global Radio spokesman said: "We can confirm that John Legg left the company before Christmas. His departure was amicable and we wish him all the best for his future career."
A senior radio source said: "John was the key touch point between the agencies and Global Radio. It is unclear who will now be replacing him and fulfilling this role. He has worked in radio for a long time and had a really good reputation with the agencies. He will really be missed."
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