Deirdre Michie, chief executive of Offshore Energies UK (OEUK), has temporarily stood back from the role after being diagnosed with a medical condition.
In a statement to member companies, Ms Michie said the issue requires “attention and treatment”.
Industry veteran and director of sustainability Mike Tholen has been appointed acting CEO.
The announcement comes after Ms Michie revealed in May that she intends to permanently stand down from the trade body, though she would not do so until a replacement had been found.
Despite the diagnosis, it is understood Ms Michie intends to return to the role to continue the search for her successor.
No further details are being disclosed about Ms Michie’s diagnosis and OEUK has asked for respect for her family’s privacy.
In her notice to members, she said: “As you know, in early July, I stated my intent to move on from OEUK at the end of 2022. Since making that announcement, I have unfortunately been diagnosed with a medical issue that requires attention and treatment.
“To ensure the continued successful delivery of OEUK, in discussions with the Co-Chairs, we have asked Mike Tholen to be Acting CEO of OEUK, taking on all responsibilities and with full delegated authority, with effect from Monday the 29th August.
“I am very grateful to Mike for taking on this role and I know you will all work to support him and the rest of the LT as we go forward.
“Thank you for your understanding and I look forward to reconnecting with you soon.”
Mike Tholen has been with the trade body for 15 years following a career with firms including Shell and Petroleum Development Oman.
In May, Ms Michie announced her intention to stand down as CEO of OEUK following eight years at the helm.
A search is underway for her permanent replacement, which OEUK has previously said they hope to have in place before the end of the year.
A veteran of oil giant Shell which she first joined in 1986, Deirdre Michie was appointed to the helm of OEUK (then Oil and Gas UK) in 2015, taking over from Malcolm Webb.
Since then she has supported the industry over the course of two huge downturns for the oil and gas sector, including the latest Covid-related price crash.
Ms Michie was awarded OBE in 2018 in recognition of her services to the oil and gas industry and was in the same year awarded a Fellowship at North East Scotland College.
One of her crowning achievements was the signing of the North Sea Transition Deal last year – a £16bn agreement between industry and government to develop low-carbon areas including hydrogen, platform electrification and carbon capture and storage (CCS).