Danny Hollands has been ruled out for up to eight weeks after breaking his leg at Ipswich Town.
It is cruel luck on the 30-year-old, who had re-established himself in the Blues side and was performing impressively.
Hollands had started the previous 14 matches, primarily alongside Michael Doyle, in a holding midfield role.
Doyle is back for Pompey tomorrow as they travel to Accrington, yet Paul Cook must decide on who will partner him.
Close was given his first start since September 1 when he lined up next to Hollands in the 2-2 draw at Portman Road.
Barton also featured in that FA Cup clash, albeit in the centre of defence.
Now both are vying to operate in Pompey’s engine room at the Crown Ground.
Cook said: ‘Losing Danny is a massive blow, it is so disappointing.
‘That middle area of the pitch is where we need to win games, it should give you the platform to go and be stronger at the top end of the pitch.
‘Danny and Michael have been doing a fantastic job over a period of time.
‘If you look at the lack of goals going in, there has been a pressure on the defensive midfielders to do a job, and the centre halves, and goalkeepers.
‘Ben Close was excellent against Ipswich, you would never know that was his first game since September, never.
‘He was another one I thought was absolutely magnificent playing against someone like Cole Skuse, who is a seasoned Championship footballer.
‘Adam is just himself. For me he has done fantastically good at the club in general.
‘I think everyone can now see the reasons why Adam was brought to the club. He’s such a talented footballer.
‘In a team like ours, if you look at Adam’s run in the team when he came in and where he is now I think he is a lot more confident within himself.
‘They both come into it. This is the thing about squads.
‘We have three games in a week now and if we make a change or two we are doing it for what we believe is the right reason.’
It took Hollands until the end of October to earn a regular run in Cook’s side.
Until that point Nigel Atangana and Barton had been given auditions.
And the boss has been delighted with the ex-Charlton man’s subsequent displays.
He added: ‘Danny was playing really well. He was excellent against Ipswich, he was excellent against Crawley.
‘A lot of the time these lads do a job people don’t really see. They do the scruffy side of the game.
‘At the moment you talk about how well Kyle Bennett is playing – and he is. But there is a balance created, which is why he is playing well.’