The important numbers and squad list restrictions that will govern what Portsmouth do before January transfer window slams shut

And one of those squad slots can be used by another loan addition at Fratton Pak, with the Blues currently having just four of the five permitted on any given match day occupied.

Of course, finances available to new head coach John Mousinho and sporting director Rich Hughes will dictate whether any new arrivals land at Fratton Park before Tuesday night’s 11pm deadline.

That number will also rise if Pompey decide to say goodbye to any of their fringe players in the four remaining days of the window.

But with the Blues and all other League One clubs restricted on the number of players they can include in their official squad lists for the remainder of the season, it gives the Fratton faithful a good idea of what’s possible between now and Tuesday evening.

Those first-team names must be submitted to the EFL within 24 hours of the transfer deadline, with the league then publishing each club’s squad and a list of all other contract players eligible to participate in matches but are not included within seven days.

Under current rules, all third and fourth-tier clubs are restricted to 22 players. However, goalkeepers or any player under the age of 21 do not count towards the 22.

At present, the Blues have 19 senior members who must be included.

Before the January window opened that number was 21. But this month’s departures of 30-year-old Michael Morrison and loanee Josh Koroma, who is 24, means Mousinho now has greater scope to add to his ranks.

Twenty-one-year-old keeper Josh Griffiths, who has also left to return to parent club West Brom, was not required to be on the Blues squad list for the first half of the season.

Meanwhile, Pompey do not have to include new arrivals Ryley Towler, 20, and 28-year-old loan stopper Matt Macey in the latest version.

Macey joins Owen Dale, Dane Scarlett and Joe Pigott in taking up four of the five loans places available in the Blues squad – with all four now guaranteed to remain at Fratton Park until the season finishes.

As mentioned, Mousinho can free up even more room in his ranks by offloading any player he doesn’t wish to keep at PO4.

However, with Tom Lowery, Jay Mingi, Clark Robertson and Joe Rafferty still ruled out through injury – and Ronan Curtis out for three weeks with an ankle problem – the new head coach is likely to resist the urge to let anyone else leave this month.

Mousinho has also said he is keen to give everyone available to him a chance to impress before making a decision on futures at the end of the season, handing anyone on the fringes a potential Fratton Park lifeline.