The former England manager took charge of the Magpies for a second spell in January 2008.
However, he lasted less than eight months in the St James' Park hot seat.
Keegan resigned as boss on September 4 '“ three days after the summer transfer window closed '“ following a breakdown in relations with owner Mike Ashley.
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On deadline day, Pompey were rumoured to be chasing Barton as they prepared for their maiden Uefa Cup campaign.
Manager Harry Redknapp rubbished the Blues were interested in the one-cap England midfielder when he was asked by The News after the window had shut.
Yet Keegan insists the Newcastle board attempted to engineer Barton a switch to Fratton Park.
The ex-Liverpool forward told Football Focus: '˜There was an owner, in my mind, at that time who had money to put in (to the club).
'˜In reality, it wasn't like that.
'˜It wasn't an owner who wanted to put money in at all.
'˜I was surrounded by people who just didn't want to help me '“ in fact, who made the job more difficult.
'˜They tried to get Michael Owen out on loan without telling me and they tried to get Joey Barton to Portsmouth.
'˜Players are coming to you saying 'gaffer, why are you doing this?'
'˜You're going back to them (the board) saying 'what are you doing guys, this is not a way to run a football club'.'