The Russian billionaire's investment vehicle which paid nearly £2bn to buy Holland & Barrett (H&B) is to replace the health food chain's chief executive after less than 18 months.
Sky News has learnt that Tony Buffin is to step down from the post imminently.
An announcement could be made as soon as Tuesday morning.
The reasons behind his sudden departure were unclear on Monday, although insiders said there had been tensions between Mr Buffin and LetterOne, the investment firm which owns H&B.
One source said that part of the friction between the two sides related to an incentive plan put in place for the chain's top executives.
The appointment of a successor to Mr Buffin, who joined from the builder's merchant Travis Perkins, is expected to be announced alongside news of his departure.
One insider said that Steve Willett, a former executive at the DIY retail group Kingfisher and a current non-executive director of H&B, might be unveiled as its next chief executive, although that could not be confirmed on Monday.
H&B is one of the world's largest specialist health and wellness retailers, with more than 1500 stores in the UK and overseas.
It was bought by L1 Retail, a vehicle created by the Russian oil billionaire Mikhail Fridman, in 2017.
H&B and LetterOne declined to comment, while Mr Buffin could not be reached.