Replacing Matt Clarke in the centre of the Pompey defence was always going to be a difficult task.
And with a new right-back also on the agenda following Nathan Thompson’s contract snub, the unenviable job of rebuilding the Blues’ back line just got that much harder.
But nearly three months into the season, it appears the extent of that challenge may have been underestimated.
At first glance, Pompey’s current defensive record might disguise any consequential problems.
With 14 goals conceded in League One to date, only Ipswich (10), Rotherham and Burton (both 13) have let in fewer.
Meanwhile, last term the Blues, with Clarke and Thompson in tow, conceded an average of 1.1 goals per game in the third tier.
At present, the rate is 1.07.
Those stats accompany a defensive reshuffle this season that has seen Jackett utilise five different central-defensive partnerships.
He’s also had to make do with a Lee Brown injury that kept him out for six weeks, while Rangers loanee Ross McCrorie currently appears the favoured option at right-back.
Yet here’s were the first sign of trouble lies.
Only one of the three defensive reinforcements brought in over the summer can actually call themselves first-team regulars.
And even then, Sean Raggett – on loan from Norwich – has had his credentials questioned by near enough everyone at Fratton Park – including Jackett.
He’s started each of Pompey’s past six games in the league, partnering Christian Burgess in central defence, as his PO4 career finally shows signs of momentum following early teething problems.
Yet, as he appears to be embarking on an upward Blues trajectory, it’s the reverse for both Paul Downing and James Bolton.
Both free transfers find themselves out of the starting XI, with Downing’s last league appearance being the 2-2 draw with Burton on September 17.
Meanwhile, Bolton was dropped following the recent 1-0 defeat to Wimbledon.
And to add salt into the wounds, Jackett has admitted extra work has been needed on the training ground to get both up to his so-called desired levels.
Hardly, a strategy fans want to hear as they look for signs of defensive solidity in the post Clarke/Thompson era.
Speaking after the Dons defeat, Jackett said of Bolton: ‘I have been pleased with him overall, but I feel at times we need somebody to bring the ball out from the back.
‘I feel full-backs have to be able to get forward and maybe burst through with pace.
‘We have been working with James, that is part of his progression.’
He said: ‘We’ve worked on all aspects of centre-half play with him.
‘Last Thursday we specifically worked on the ball down and delivery forward to the front men.
‘I wouldn’t say it has been a big weakness, but it is where I feel that, at the right time, service into the front men is something he is capable of – and we have worked on it.’
And all that follows real scrutiny of Raggett’s game, with the manager saying back in September: ‘We have done a lot of work with him, a lot of sprinting, turning, all those type of things, all aspects of centre-half play.
‘Whether that be physical, technical or video work – which is tactical – we try to cover everything, to provide the information he needs and the work he needs. This is back-up, extra stuff at the training ground.’
When these particular signings were announced in the summer, Pompey fans would have been forgiven for thinking all three were finished products and capable of taking the Blues up a level.
The players themselves, would have been confident of filling the voids left behind, with Downing, in particular, arriving with a big reputation.
But, through no fault of their own, the evidence suggests the Blues are still searching for ways to replace Clarke and Thompson.