Club owner Mike Ashley did not trust Sam Allardyce to bring in the players who could turn around Newcastle's flagging season, according to close friend Paul Kemsley.
Allardyce left the club by mutual consent last night after just 24 games and eight months in charge on Tyneside.
Reports have suggested his departure came just hours after a meeting with club's hierarchy to discuss possible transfer activity in the current window.
The former Bolton boss enjoyed little success with the new faces he brought in last summer, with the likes of Joey Barton, Alan Smith, Claudio Cacapa and Jose Enrique struggling to make an impact.
Ashley backed Allardyce with cash despite the fact he had been appointed before the billionaire's takeover last July.
But Kemsley, the former Tottenham vice-chairman, believes Ashley was unwilling to do so again.
'People have got realise that Sam Allardyce was not Mike's choice, Mike bought the club with him already employed,' he told BBC Radio Five Live.
'Mike took the view that he is in the job, let's see if he can deliver what I want, which is good-quality, attacking football and to win games. I'll give him time to see if he can deliver that.
'Mike has put £250million into the club and is about to invest more, no doubt, in the window, and I suspect he wants to invest that in his own man and his own team.'
Ashley has been widely criticised for the timing of Allardyce's exit, with some suggesting he might have been swayed into premature action by the disenchanted Toon Army, with whom he famously sits to watch matches.
But Kemsley insists there is no way he would have rushed a decision purely because of supporter unrest.
'Mike's a very considered guy,' he added. 'It (running Newcastle) is certainly costing a lot more initially than he thought it would.
'He, along with everybody else at Newcastle, wants to see good-quality football, they want to win, and he's a winner.
'It's a difficult decision whenever you get rid of a manager and there are always a thousand opinions. But he thought about it and decided it was in the best interests of the football club.
'I know Mike well enough to know that he doesn't make decisions rashly.
'He will know where he's going, he will stick to his plans and deliver what he believes will please the Newcastle fans.
'If you give him time, he will deliver exactly what the Newcastle fans want. I'm sure he's got a plan.'