Sir Jim Ratcliffe is expected to ask an external auditor to assess Manchester United’s structure and expenditure with a view to executing a major streamlining exercise, meaning as many as 300 jobs are potentially under threat.

Executives from Ineos have been in discussions with United over the past weeks regarding Ratcliffe’s plans ahead of his 25% purchase of the club becoming official on Christmas Eve, with the club’s management already having been reminded to curb rising costs to ensure maximum funds for transfers within the strictures of financial fair play.

Related: From Ten Hag’s future to a leaking roof: Ratcliffe’s Manchester United in-tray

The 71-year-old believes staff numbers, which are a minimum of 1000, could be reduced by between 25-30% and so will instruct a blue chip accountant to audit the club. This may be one of the so-called big four of KPMG, Deloitte, Ernst & Young or PwC. In 2019 Ineos changed from PwC, its longstanding auditor, to Deloitte but whether the latter company will work on United is unclear.

Staff at the club are aware that the change in ownership structure means a review of the number of employees and departments. Senior managers have already been reminded of the need for cost discipline to ensure expenditure is kept to a minimum to maximise funds for player acquisition. This is not a formal cost-cutting strategy but a decision taken within the context of FFP rules having been tightened.

Although, as part of his 25% purchase, Ratcliffe will inject $300m (£237m) into United this is for infrastructure and not to strengthen the squad of Erik ten Hag, the manager. The deal will not be ratified by the Premier League until after the January transfer window.

Ratcliffe has written to the Manchester United Supporters’ Trust, the Fans’ Forum and the Fans’ Advisory Board stating that Ineos “are in it for the long-term” and while he takes his responsibility gravely, any success will require time.

He said: “I believe we can bring sporting success on the pitch to complement the undoubted commercial success that the club has enjoyed. It will require time and patience alongside rigour and the highest level of professional management.

“You are ambitious for Manchester United and so are we. There are no guarantees in sport, and change can inevitably take time but we are in it for the long term and together we want to help take Manchester United back to where the club belongs, at the very top of English, European and world football. I take that responsibility very seriously.”

Shares in United rose by 3% on Tuesday after Ratcliffe’s stake was confirmed. They have gone up around 52% since the Glazer family announced in November last year that they were exploring strategic options, including a sale, for the club.