Newcastle United manager Rafael Benitez will have £30m to spend in the January transfer window thanks to Amanda Staveley's impending takeover at St James' Park.

Staveley's PCP Capital Partners firm has increased their offer to £300m which is expected to be accepted by current owner Mike Ashley, leading to the end of his 10-year association with the north east side.

A four-week period of due diligence and the completion of the Premier League's fit and proper persons test is required for the takeover to be finalised, a process which could take four weeks.

Those procedures could be extended during the Christmas and New Year period meaning the January transfer window may have all but closed before Newcastle have the chance to benefit from Staveley's arrival.

The Guardian understand that Ashley will fit the bill for the improvements Benitez wants to make to his squad – to the tune of around £30m – with Staveley's reimbursing him for the investment.

Benitez has already identified a number of targets and held talks over Newcastle's approach in January with managing director Lee Charnley but is uncertain over the size of his budget.

But as Staveley is worried Newcastle could be involved in a relegation battle in the New Year with the club 16th in the table after six defeats in their last seven games, she has agreed a deal which will see her finance any new signings.

While the exit of Ashley after a decade at Newcastle will be greeted with much delight, news that the takeover will not prohibit the club from investing in the transfer market will come as great relief to Benitez.

"We are monitoring players but at the moment we don't know how much money is available," the Spaniard said, according to Sky Sports, on Tuesday [12 December] when asked about his possible transfer budget. "All we can do is concentrate on football and the games.

"We don't know what the budget is. We know what we need. But can we get that? I don't know.

"It is always helpful if you have information. Hopefully after the Everton game and a win we will have good news and everybody will be happy.

"It is important to know because we are working really hard with the scouts. We have a lot of names, but we do not know exactly how much we have.

"I was asking Lee Charnley the other day and I am waiting for an answer in a few days.

"A lot of teams around of us have spent a lot of money and are still around us. We need to stay calm, work harder and we will start winning games."